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Recurrent episodes of severe bleeding caused by congenital factor XIII deficiency in a dog Lyndsay R. Kong, DVM; Elisabeth C. R. Snead, DVM, MSc; Hilary Burgess, DVM, DVSc; Marc P. Dhumeaux, DEDV, MVSc
Case Description—A 5-year-old castrated male Toy Poodle cross was evaluated because of lethargy, inappetence, and suspected abdominal hemorrhage. The dog had been evaluated on 4 other occasions for episodes of excessive bleeding associated with trauma or surgical procedures. Clinical Findings—At previous evaluations, results of repeated measurements of prothrombin time, partial thromboplastin time, and buccal mucosal bleeding time were unremarkable; activated clotting time, plasma von Willebrand factor concentration, results of platelet function testing, and plasma factor VII, VIII, IX, X, XI, and XII concentrations were considered normal. At this evaluation, clinicopathologic analyses revealed mild regenerative anemia that progressed over a 4-day period to moderate regenerative anemia and acute inflammation with panhypoproteinemia. Abdominal ultrasonography revealed a large mass (suspected to be a hematoma) near the urinary bladder. Rotational thromboelastometry revealed that clotting times were within reference limits, with abnormal clot formation times and clot firmness. The result of a factor XIII (FXIII) clot solubility assay confirmed FXIII deficiency. Treatment and Outcome—The dog’s bleeding diathesis resolved with inpatient care and IV fluid therapy, although plasma transfusions had been required at previous evaluations. Seven months after discharge from the hospital, the dog continued to do well clinically, although it had several additional episodes of excessive bleeding. Clinical Relevance—To the authors’ knowledge, this is the first reported case of congenital FXIII deficiency in a dog. In addition to more common inherited coagulopathies, FXIII deficiency should be a differential diagnosis for dogs with episodes of excessive bleeding and apparently normal results of standard coagulation tests. (J Am Vet Med Assoc 2014;245:1147–1152)
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5-year-old 10.2-kg (22.4-lb) castrated male Toy Poodle cross was evaluated at the Veterinary Medical Centre at the Western College of Veterinary Medicine on an emergency basis because of lethargy and decreased appetite of 4 days’ duration and suspected abdominal bleeding. The dog was administered IV fluid therapy (lactated Ringer’s solution; 15 mL/h) and cefazolin (22 mg/kg [10 mg/lb], IV, q 8 h) by the referring veterinarian starting 2 days prior to the evaluation. Two brief abdominal ultrasonographic examinations performed by the referring veterinarian 2 days and 1 day prior to this evaluation revealed accumulating free fluid. Abnormal hematologic findings included mild regenerative anemia (RBC count, 5.08 X 1012 RBCs/L [reference range, 5.20 X 1012 RBCs/L to 8.20 X 1012 RBCs/L]; Hct, 0.335 L/L [reference range, 0.365 to 0.573 L/L]; and proportion of reticulocytes, 2.5%) and evidence of acute inflammation (WBC count, 22.1 X 109 WBCs/L From the Departments of Small Animal Clinical Sciences (Kong, Snead, Dhumeaux) and Pathology (Burgess), Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada. Dr. Kong’s present address is Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE C1A 4P3, Canada. Dr. Dhumeaux’s present address is Pride Veterinary Centre, Riverside Rd, Pride Park, Derby DE24 8HX, England. The authors thank Dr. Robert Devaraj for assistance with the factor XIII clot solubility assay. Address correspondence to Dr. Kong ([email protected]). JAVMA, Vol 245, No. 10, November 15, 2014
ABBREVIATIONS aPTT CFT FXIII MCF PT
Activated partial thromboplastin time Clot formation time Factor XIII Maximum clot firmness Prothrombin time
[reference range, 4.80 X 109 WBCs/L to 13.9 X 109 WBCs/L]; neutrophil count, 16.796 X 109 neutrophils/L [reference range, 3.0 X 109 neutrophils/L to 10 X 109 neutrophils/L]; and band neutrophil count, 2.431 X 109 band neutrophils/L [reference range, 0.0 X 109 band neutrophils/L to 0.1 X 109 band neutrophils/L]; slight toxic change detected). Panhypoproteinemia (total protein concentration, 44 g/L [reference range, 55 to 71 g/L]; albumin concentration, 29 g/L [reference range, 32 to 42 g/L]; and globulin concentration, 15 g/L [reference range, 20 to 34 g/L]) was identified via serum biochemical analysis. The dog subsequently developed hematuria and was referred to the Veterinary Medical Centre for a possible blood transfusion. The dog had no history of trauma prior to evaluation by the referring veterinarian on this occasion, but pertinent past medical history included several episodes of excessive bleeding associated with trauma or surgical procedures. At 6 months of age, scrotal hemorrhage occurred after the dog was neutered. The surgical Scientific Reports
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incision was reopened multiple times over the following 5 days to remove blood clots, and a blood transfusion was required 6 days after neutering. At that time, the dog’s platelet count was estimated as normal (automated count, 111 X 109 platelets/L; reference range, 200 X 109 platelets/L to 900 X 109 platelets/L) with platelet clumps on blood smear examination. Plasma concentration of von Willebrand factor antigen was within reference range (76%; reference range, 45% to 180%). The PT was not prolonged (7.1 seconds; reference range, 7.5 to 9.9 seconds), and the aPTT, although mildly prolonged (13.9 seconds; reference range, 9.6 to 13.8 seconds), was not deemed sufficiently high to be responsible for the amount of hemorrhage seen. At 9 months of age, the dog was evaluated by the Veterinary Medical Centre ophthalmology service; a presumptive diagnosis of congenital glaucoma that was nonresponsive to medical management necessitated left eye enucleation. Results of preoperative hematologic and serum biochemical analysis and buccal mucosal bleeding time (< 4 minutes; reference range,1 1.7 to 4.2 minutes) were apparently normal. The dog underwent blood typing and cross-matching prior to surgery. Minimal hemorrhage occurred during surgery, but moderate oozing of blood was noted from the enucleation incision after surgery. The dog’s PCV was 41% (reference range, 36.5% to 57.3%). Given that its condition appeared stable, the dog was discharged from the hospital. However, the dog was reevaluated that evening because of excessive bleeding from the surgical site. The PT (7.7 seconds), aPTT (13.3 seconds), and activated clotting time (< 120 seconds; reference range,2 60 to 125 seconds) were all within reference limits. The dog’s PCV had decreased to 25%; hence, the dog was administered diphenhydramine (2 mg/kg [0.9 mg/lb], IM) and a transfusion of stored whole blood (110 mL). Histologic evaluation of the enucleated eye confirmed congenital glaucoma. Two weeks after the enucleation, the dog was evaluated at a private veterinary clinic because of signs of pain on opening its mouth and signs of depression; palpation of the left side of the face elicited signs of pain. The dog was sedated, and an examination of the oral cavity was performed. The examination revealed a swelling at the left caudal aspect of the mouth, which, on aspiration, was found to contain blood. The dog was again referred to the Veterinary Medical Centre, but no treatment was given because the mass was resolving. The mass was attributed to hemorrhage secondary to a hitherto undiagnosed coagulopathy. A platelet function testa was performed, and results were considered normal (96 seconds; reference range,3 48 to 105 seconds). At 2 years of age, the dog was evaluated at another private veterinary clinic because of a bite wound to the abdomen. The dog developed a subcutaneous hematoma near its right quadriceps femoris muscle, along with extensive bruising on the ventral aspect of the abdomen and in the inguinal region, and was referred to the Veterinary Medical Centre for evaluation of excessive bleeding that resulted in moderate regenerative anemia (RBC count, 3.8 X 1012 RBCs/L; Hct, 0.259 L/L; and proportion of reticulocytes, 6.1%). The platelet count, PT, aPTT, and buccal mucosal bleeding time were again within reference ranges. To verify the findings of the 1148
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screening test at our laboratory and to rule out a mild factor deficiency not detected by the PT and aPTT testing, screening coagulation tests were repeated, and specific factor assay testing was performed through the Cornell University Animal Health Diagnostic Center. These analyses revealed no abnormalities, as follows: aPTT, 12.1 seconds (reference range, 10 to 17 seconds); PT, 14.6 seconds (reference range, 11 to 16 seconds); thrombin clotting time, 6.0 seconds (reference range, 5 to 9 seconds); plasma von Willebrand factor antigen concentration, 143% (reference range, 70% to 180%); plasma factor VII concentration, 118% (reference range, 50% to 150%); plasma factor VIII concentration, 87.5% (reference range, 50% to 200%); plasma factor IX concentration, 86% (reference range, 50% to 150%); plasma factor X concentration, 87% (reference range, 80% to 175%); plasma factor XI concentration, 97% (reference range, 60% to 150%); and plasma factor XII concentration, 92% (reference range, 60% to 150%). Given the undefined nature of the dog’s hemostatic defect, the owners were told to expect further bleeding episodes following any type of trauma and that administration of fresh frozen plasma would be necessary prior to any surgical procedure. Differential diagnoses for the dog’s bleeding disorder included a deficiency in antifibrinolytic proteins, a rare platelet function defect (eg, Scott syndrome), or a deficiency in FXIII; however, the owners declined further investigation. At 3 years of age, the dog was again referred to the Veterinary Medical Centre because of a bite wound to its right ear that developed into a severe aural hematoma. During the 3 days preceding referral, the dog’s PCV had decreased from 45.5% to 29.2%, and its platelet count decreased from 275 X 109 platelets/L to 48 X 109 platelets/L (reference range, 200 X 109 platelets/L to 900 X 109 platelets/L). The PT and aPTT were again within reference ranges. The hematoma eventually resolved with repeated application of pressure bandages over a 4-day period of hospitalization. Although FXIII deficiency testing was recommended at this time, the owners failed to bring the dog back for the necessary follow-up. At the current evaluation, the dog was lethargic, and signs of pain were elicited during abdominal palpation. There were mild areas of ecchymotic hemorrhage on the right side of the abdominal wall. Abdominal ultrasonography revealed subcutaneous edema, moderate peritoneal effusion, and a hypoechoic mass near the urinary bladder. The dog was hospitalized. During a period of 4 days, the dog’s initial mild regenerative anemia progressed to moderate regenerative anemia (RBC count, 3.46 X 1012 RBCs/L; Hct, 0.239 L/L; and proportion of reticulocytes, 4.4%). The dog also developed thrombocytopenia (platelet count decreased from estimated normal to between 25 X 109 platelets/L and 100 X 109 platelets/L) during that period. The mass near the urinary bladder was suspected to be a hematoma or an intra-abdominal neoplasm on the basis of findings of repeated abdominal ultrasonographic examinations. Collection of aspiration or biopsy specimens of the mass could not be performed because of the dog’s coagulopathy and current thrombocytopenia. Rotational thromboelastometryb and an FXIII clot solubility assay were performed to further investigate JAVMA, Vol 245, No. 10, November 15, 2014
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the cause of the dog’s underlying coagulopathy. Thromboelastometry is an in vitro diagnostic technique that can continuously record changes in the viscoelastic properties of whole blood during clotting and fibrinolysis. It has clinical applications for diagnosis of hypercoagulable states, platelet function disorders, and defects in fibrin formation and fibrinolysis via a series of assays: an extrinsic pathway assay with tissue factor reagent (Figure 1), an intrinsic pathway assay with ellagic acid reagent (Figure 2), and a fibrinolysis assay with cytochalasin D in DMSO solution and 0.2M CaCl2 in HEPES buffer (pH, 7.4; Figure 3). Although the dog had normal clotting times (measured in seconds from clot initiation to a clot amplitude of 2 mm) for thromboelastometry assays evaluating the extrinsic (43 seconds; reference range, 29 to 75 seconds) and intrinsic (139 seconds; reference range,4 129 to 200 seconds) pathways, CFT (measured in seconds from a clot amplitude of 2 to 20 mm) could not be determined in the extrinsic pathway assay (reference range,4 66 to 186 seconds) because the clot did not reach an amplitude of 20 mm and was delayed in the intrinsic pathway assay (744 seconds; reference range,4 48 to 237 seconds). The MCF (maximum clot amplitude) was decreased for all assays (extrinsic pathway assay, 19 mm [reference range,4 46 to 63 mm]; intrinsic pathway assay, 22 mm [reference range,4 45 to 64 mm]; and fibrinolysis assay, 4 mm [reference range,5 6 to 26 mm]). Assessment of the rotational thromboelastometry tracings revealed a small clot with a decreased slope of the line delimiting the α angle, indicating slow clot formation. A citrated blood sample from this dog along with a sample from an ageand breed-matched clinically normal dog was sent to Regina General Hospital to undergo an FXIII clot solubility assay. The clot solubility assay determines the interval to lysis of a stabilized clot after addition of either a 1% monochloroacetic acid or 5M urea solution; in blood samples obtained from individuals with an FXIII deficiency, clot lysis time is shortened (ie, < 24 hours) owing to poor cross-linking of the fibrin clot. Results of this test were abnormal (clot dissolution occurred within 24 hours following incubation) for the sample from the dog of this report and were normal (the clot remained stable after 24 hours of incubation) for the sample from the control dog. The dog was treated IV with isotonic electrolyte solutionc supplemented with
Figure 1—Extrinsic pathway thromboelastogram obtained for a 5-year-old Toy Poodle cross that was evaluated because of lethargy and decreased appetite of 4 days’ duration and suspected abdominal bleeding. The dog had been evaluated on 4 other occasions because of episodes of excessive bleeding associated with trauma or surgical procedures. Specific coagulation factor testing subsequently confirmed that the dog had an FXIII deficiency. The clotting time (measured in seconds from clot initiation to a clot amplitude of 2 mm, end point demarcated by the change from dark gray to light gray) is within reference limits (43 seconds; reference range, 29 to 75 seconds), but CFT (measured in seconds from a clot amplitude of 2 to 20 mm) could not be determined because the clot amplitude never reached 20 mm. The slope of the line represents the α angle (the rate of clot formation), which was low (26°; reference range, 58° to 76°). The MCF (maximum clot amplitude) is also decreased (19 mm; reference range, 46 to 63 mm). Dashed lines represent the lower reference limit for MCF.
Figure 2—Intrinsic pathway thromboelastogram obtained for the same dog as in Figure 1. The clotting time (end point demarcated by the change from dark gray to gray) is within reference limits (139 seconds; reference range, 129 to 200 seconds), but CFT (end point demarcated by the change from gray to light gray) is markedly prolonged (744 seconds; reference range, 48 to 237 seconds). The slope of the line represents the α angle, which is low (36°; reference range, 52° to 78°). The MCF is decreased (22 mm; reference range, 45 to 64 mm). Dashed lines represent the lower reference limit for MCF.
Figure 3—Fibrinolysis thromboelastogram obtained for the same dog as in Figure 1. The MCF is low (4 mm; reference range, 6 to 26 mm), and visually, the clot amplitude appears uniformly decreased. Dashed lines represent the lower reference limit for MCF. Scientific Reports
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20 mEq of KCl/L (26 mL/h) from the day of admission until discharge. The dog was discharged from the hospital 5 days after evaluation. The owners were instructed to return the dog for follow-up ultrasonography in 1 month. Two months later, the dog was evaluated by its regular veterinarian for routine vaccination. Findings of follow-up ultrasonography of the abdomen performed by the referring veterinarian at that time were unremarkable. Following vaccination, the dog developed a large subcutaneous hematoma leading to non–weightbearing lameness, which subsequently resolved. Five months after vaccination, the dog jumped out of a car, resulting in severe abdominal hemorrhage that limited its ability to walk; ambulation was assisted with sling support, and the dog did not require hospitalization. The injury resolved. At the time of the injury, hematologic analysis revealed moderate anemia (RBC, 3.47 X 1012 RBCs/L [reference range, 5.50 X 1012 RBCs/L to 8.50 X 1012 RBCs/L]; Hct, 0.223 L/L [reference range, 0.370 to 0.550 L/L]). An ultrasonographic examination performed a week later confirmed resolution of the bleeding. Discussion Factor XIII deficiency is a coagulopathy that is rare in people6 and, to the authors’ knowledge, has not been previously described for domestic animals. Factor XIII is involved in stabilizing the initial fibrin clot formed during secondary hemostasis. Clinical signs of congenital FXIII deficiency in people include umbilical stump bleeding; hemarthrosis; poor wound healing; bleeding after surgery, minor trauma, or strenuous exercise; recurrent miscarriages; and intracranial bleeding.7,8 The latter is a major cause of death and disability in affected humans. This case report is the first to describe congenital FXIII deficiency in a dog with multiple episodes of severe bleeding starting from a young age. Factor XIII is the final coagulation factor in the coagulation cascade and because of its function is referred to as the fibrin-clot stabilizing factor. It circulates in plasma as a tetramer of 2 catalytic A subunits and 2 carrier B subunits (A2B2). Thrombin, together with Ca2+, fibrin, and fibrinogen, activates FXIII by cleavage of the activation peptide from the A subunit.9 The final step in activation, which involves dissociation of the A subunits from the B subunits, is also greatly accelerated by Ca2+ and fibrin. Activated FXIII then covalently cross-links fibrin polymers, converting them from loose polymers into an organized clot.9 Through this process, the stable fibrin clot is able to firmly adhere to the underlying wound so that it is not easily dislodged by shear stress. In addition, activated FXIII incorporates antifibrinolytic proteins such as α2-antiplasmin into the clot to help prevent premature degradation of the clot by the fibrinolytic system.9 The recurrent episodes of excessive hemorrhage over a period of several years in the dog of this report were highly suggestive of an inherited coagulopathy; however, pedigree information for the dog’s sire and dam was not available, and this dog was the only puppy born alive in that litter. Commonly used screening tests 1150
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ruled out well-known coagulopathies early, leaving only a few remaining possible differential diagnoses (rare platelet function defect; a deficiency in plasminogen activator inhibitor-1, α2-antiplasmin, or thrombin-activated fibrinolysis inhibitor [the latter leading to a hyperfibrinolytic state]; and an FXIII deficiency). A thrombopathy was less likely on the basis of the dog’s apparently normal result on platelet function testing,a which has a high reported sensitivity (95.7%) and specificity (100%) with use of the ADP-collagen cartridgea for detection of a platelet function defect in dogs; however, because the platelet function testa may not consistently detect milder forms of platelet dysfunction and certain platelet disorders (storage pool disease or Scott syndrome),11,12 a platelet function abnormality was not definitively ruled out on the basis of this result. The platelet function testa can also be used to detect abnormalities in von Willebrand factor function; normal test results for this dog made a von Willebrand factor dysfunction unlikely.13 Rotational thromboelastometry findings also conclusively ruled out both a thrombocytopathia and a fibrinolytic system abnormality, and the clot solubility test confirmed the dog’s FXIII deficiency. On the basis of a search of the veterinary medical literature, this is the first reported case of congenital FXIII deficiency in a dog, to the authors’ knowledge. Congenital FXIII deficiency in humans has been reported,14 and knockout mice have been bred specifically for an FXIII deficiency.15 In people, it is considered a rare coagulation disorder that has a much lower incidence than either hemophilia A or B6 and most commonly results from a deficiency in the A subunits (type 2 defect), although it can also result from a lack of B subunits (type 1 defect).9 Patients with congenital FXIII deficiency have a severe bleeding diathesis, typically apparent after trauma. Bleeding after a traumatic event will often be delayed because the blood clots formed are loose and therefore contribute to rebleeding when not stabilized. This diathesis and delay in onset of bleeding were evident in the dog described in the present report, wherein all but 1 incidence of abnormal bleeding were subsequent to surgical or accidental trauma and bleeding was often delayed following surgical procedures. In addition to its hemostatic role, FXIII is also important for maintenance of pregnancy, for wound healing and tissue repair, and for angiogenesis.16 Recurrent miscarriages are common in affected women.7 In affected people, wound healing occurs extremely slowly; thus, wounds continue to bleed for a prolonged period (as long as several weeks) despite surgical intervention or compressive bandages, similar to the clinical features of the case described in this report. Diagnosis of FXIII deficiency is challenging because the most commonly used results of screening tests for primary and secondary hemostatic diatheses are expected to be normal.17 Tests for secondary hemostasis (PT and aPTT) detect only the appearance of polymerized fibrin but not its stabilization by FXIII. In the dog of this report, the repeatedly unremarkable PT, aPTT, and thrombin clotting time made abnormalities in factors I, II, V, VII, VIII, IX, X, XI, XII, prekallikrein, and high-molecular-weight kininogen unlikely,18 although a mild factor deficiency could not be conclusively ruled JAVMA, Vol 245, No. 10, November 15, 2014
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deficiency in the case described in this report because the data can reflect abnormalities with fibrin formation and cross-linking. Thromboelastography incorporates different assays that evaluate the intrinsic or contact pathway (analogous to aPTT assessment), the extrinsic or tissue factor pathway (analogous to PT assessment), and fibrinolysis (by irreversibly inhibiting platelets with cytochalasin D to eliminate the platelet contribution to clot formation).21 Thromboelastometry, a modification of thromboelastography, was used to test the patient in this report. Clotting time is primarily a function of coagulation factor concentrations, whereas CFT and MCF rely more on platelet function and fibrin formation and cross-linking.22 Normal clotting time, with delayed CFT and decreased MCF, as detected in the dog of this report, was consistent with either an FXIII deficiency or platelet abnormality. Thrombocytopenia at the time of testing could have influenced these results by falsely increasing CFT and decreasing MCF as determined by the intrinsic and extrinsic pathway assays; however, the fibrinolysis assay removes platelet contribution to clotting, and concurrent abnormal MCF results determined by the fibrinolysis assay ruled out thrombocytopenia (along with other platelet abnormalities) at the time of testing as a sole cause for abnormal CFT and MCF revealed by the intrinsic and extrinsic pathway assays. Thromboelastography has been validated as a specific and sensitive test for detection of FXIII deficiency in people.23 Thromboelastometry, as a modification of thromboelastography, is assumed to have similar sensitivity and specificity, and it was the only test other than the clot solubility test that yielded abnormal findings in this dog; therefore, thromboelastometry should be considered a useful diagnostic tool for investigating a coagulopathy where the underlying cause is not evident on the basis of standard screening test results. Treatment of humans with FXIII deficiency traditionally consists of cryoprecipitate or fresh frozen plasma transfusions administered every 4 to 6 weeks. More recently, a new treatment that uses plasma-derived pasteurized FXIII concentrate has been available.9 The only treatment option currently available for veterinary patients would be frequent administration of either cryoprecipitate or fresh frozen plasma given the lack of species-specific FXIII concentrate. Prevention of bleeding by means of intermittent administration of cryoprecipitate has been attempted in humans,9 but this may not be financially viable for many veterinary clients. Gene therapy has been explored as a possible treatment option in dogs with hemophilia B (factor IX deficiency)24 or hemophilia A (factor VIII deficiency)25 and may represent an area for future research. In the case described in this report, treatment included advising the owners to minimize or prevent any traumatic events and providing transfusions to stabilize the dog after episodes of bleeding. Factor XIII deficiency may be considered as a differential diagnosis in dogs with a coagulopathy that is not detected by standard coagulation screening tests. A thorough evaluation for more common inherited coagulopathies (von Willebrand disease, hemophilia A, and hemophilia B) should be performed before considering FXIII testing. Platelet function testing and rotational thromboelastometry may be helpful diagnostic Scientific Reports
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out prior to specific factor testing. Although PT and aPTT are reliably used to detect severe deficiencies in clotting factors associated with secondary hemostasis, both tests have relatively low sensitivity (30%) for detection of mild factor deficiencies, and such sensitivities can vary depending on the deficient factor and the reagent used in the tests.19,20 Possible deficiencies in factors VII through XII were conclusively ruled out through factor testing for the dog of this report. In addition, patients with an FXIII deficiency will have a platelet count, platelet function test results, and plasma von Willebrand factor antigen concentration that are all within reference limits, as seen in the dog of this report, thereby ruling out common primary hemostatic disorders. Although the dog was thrombocytopenic during 2 episodes of bleeding, this was likely a result of platelet consumption during excessive hemorrhage. Platelet count was within reference range at most evaluations, ruling out thrombocytopenia as a cause of the dog’s excessive bleeding. A clot solubility test has been traditionally used to diagnose an FXIII deficiency in people.9 For this test, a plasma sample from an affected patient is incubated with a buffer of calcium and thrombin to promote clot stabilization. The clot is then suspended in a freshly prepared solution of either 1% monochloroacetic acid or a 5M urea solution and left undisturbed at 37°C for 24 hours. In a patient with normal FXIII concentration, the clot remains stable after 24 hours. Clot lysis occurs rapidly (typically within hours) when an FXIII deficiency exists because the fibrin clot formed is poorly crosslinked and dissolves more quickly.9 Controls (blood samples from apparently normal individuals) must also be run when the test is performed, and considering that the test is manual, it must be performed in duplicate. Owing to the semiquantitative nature of this assay, only severe FXIII deficiencies (activity of FXIII, < 1% of activity in a clinically normal individual) may be detected, which can delay diagnoses in some humans with less severe deficiencies.8 Even the addition of a small amount of plasma from a healthy individual to the test system will elevate FXIII activity to 1% to 3% of that expected in clinically normal individuals and render the clot insoluble. Hence, this test should not be run if plasma has been administered to the patient within the preceding few weeks. Despite this shortcoming, the clot solubility test is still used by many laboratories for the diagnosis of an FXIII deficiency in humans because of its simplicity and the lack of readily available and more quantitative diagnostic tests. Confirmation of the diagnosis, especially for mild or moderate deficiencies of FXIII, is ideally provided by use of a more quantitative test that measures FXIII activity or antigen concentration.8 As part of the diagnosis of FXIII deficiency, PCR testing has been used in to identify the specific type of mutation (A or B subunit) responsible. Because there are no dog-specific assays for determining plasma FXIII activity or antigen concentration, the clot solubility test was used to establish the diagnosis for the dog of this report. Testing for a specific subunit deficiency in this dog was not done for financial and practical reasons. Results of rotational thromboelastometry proved useful in helping to support the diagnosis of an FXIII
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tools, but specific testing for an FXIII deficiency in dogs currently relies on an abnormal clot solubility test. No highly practical or affordable treatment options are currently available for veterinary patients with FXIII deficiency, but prophylactic treatment with fresh frozen plasma transfusions should be provided before any elective or emergency surgical procedure, and owners should be warned that bleeding after trauma, even minor trauma associated with vaccination, is possible. a. b. c.
PFA-100 collagen/ADP cartridge, Siemens, Malvern, Pa. ROTEM, Pentapharm, Munich, Germany. Normosol-R, Hospira, Lake Forest, Ill.
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Jergens AE, Turrentine MA, Kraus KH, et al. Buccal mucosa bleeding times of healthy dogs and of dogs in various pathologic states, including thrombocytopenia, uremia, and von Willebrand’s disease. Am J Vet Res 1987;48:1337–1342. 2. Byars TD, Ling GV, Ferris NA, et al. Activated coagulation time (ACT) of whole blood in normal dogs. Am J Vet Res 1976;37:1359–1361. 3. Burgess HJ, Woods JP, Abrams-Ogg ACG, et al. Evaluation of laboratory methods to improve characterization of dogs with von Willebrand disease. Can J Vet Res 2009;73:252–259. 4. Smith SA, McMichael M, Galligan A, et al. Clot formation in canine whole blood as measured by rotational thromboelastometry is influenced by sample handling and coagulation activator. Blood Coagul Fibrinolysis 2010;21:692–702. 5. Falco S, Bruno B, Maurella C, et al. In vitro evaluation of canine hemostasis following dilution with hydroxyethyl starch (130/0.4) via thromboelastometry. J Vet Emerg Crit Care (San Antonio) 2012;22:640–645. 6. Ichinose A. Physiopathology and regulation of factor XIII. Thromb Haemost 2001;86:57–65. 7. Karimi M, Bereczky Z, Cohan N, et al. Factor XIII deficiency. Semin Thromb Hemost 2009;35:426–438. 8. Anwar R, Miloszewski KJA. Factor XIII deficiency. Br J Haematol 1999;107:468–484. 9. Hsieh L, Nugent D. Factor XIII deficiency. Haemophilia 2008;14:1190–1200. 10. Callan MB, Giger U. Assessment of a point-of-care instrument for identification of primary hemostatic disorders in dogs. Am J Vet Res 2001;62:652–658.
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11. Harrison P, Mackie IJ, Joseph J, et al. Performance of the platelet function analyser PFA-100 in testing abnormalities of primary haemostasis. Blood Coagul Fibrinolysis 1999;10:25–31. 12. Brooks MB, Randolph J, Warner K, et al. Evaluation of platelet function screening tests to detect platelet procoagulant deficiency in dogs with Scott syndrome. Vet Clin Pathol 2009;38:306– 315. 13. Favaloro EJ. The utility of the PFA-100 in the identification of von Willebrand disease: a concise review. Semin Thromb Hemost 2006;32:537–545. 14. Burrows RF, Ray JG, Burrows EA. Bleeding risk and reproductive capacity among patients with factor XIII deficiency: a case presentation and review of the literature. Obstet Gynecol Surv 2000;55:103–108. 15. Lauer P, Metzner HJ, Zettlmeissl G, et al. Targeted inactivation of the mouse locus encoding coagulation factor XIII-A: hemostatic abnormalities in mutant mice and characterization of the coagulation deficit. Thromb Haemost 2002;88:967–974. 16. Schroeder V, Kohler HP. New developments in the area of factor XIII. J Thromb Haemost 2013;11:234–244. 17. Bolton-Maggs PH. The rare inherited coagulation disorders. Pediatr Blood Cancer 2013;60(suppl 1):S37–S40. 18. Triplett DA. Coagulation and bleeding disorders: review and update. Clin Chem 2000;46:1260–1269. 19. Mischke R. Activated partial thromboplastin time as a screening test of minor or moderate coagulation factor deficiencies for canine plasma: sensitivity of different commercial reagents. J Vet Diagn Invest 2000;12:433–437. 20. Mischke R, Diedrich M, Nolte I. Sensitivity of different prothrombin time assays to factor VII deficiency in canine plasma. Vet J 2003;166:79–85. 21. Velik-Salchner C, Schnürer C, Fries D, et al. Normal values for thrombelastography (ROTEM) and selected coagulation parameters in porcine blood. Thromb Res 2006;117:597–602. 22. Smith SA, McMichael MA, Gilor S, et al. Correlation of hematocrit, platelet concentration, and plasma coagulation factors with results of thromboelastometry in canine whole blood samples. Am J Vet Res 2012;73:789–798. 23. Schroeder V, Chatterjee T, Kohler H. Influence of blood coagulation factor XIII and FXIII Val34Leu on plasma clot formation measured by thrombelastography. Thromb Res 2001;104:467–474. 24. Kay MA, Rothenberg S, Landen CN, et al. In vivo gene therapy of hemophilia B: sustained partial correction in factor IX-deficient dogs. Science 1993;262:117–119. 25. Connelly S, Mount J, Mauser A, et al. Complete short-term correction of canine hemophilia A by in vivo gene therapy. Blood 1996;88:3846–3853.
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Recurrent episodes of severe bleeding caused by congenital factor XIII deficiency in a dog Lyndsay R. Kong, DVM; Elisabeth C. R. Snead, DVM, MSc; Hilary Burgess, DVM, DVSc; Marc P. Dhumeaux, DEDV, MVSc
Case Description—A 5-year-old castrated male Toy Poodle cross was evaluated because of lethargy, inappetence, and suspected abdominal hemorrhage. The dog had been evaluated on 4 other occasions for episodes of excessive bleeding associated with trauma or surgical procedures. Clinical Findings—At previous evaluations, results of repeated measurements of prothrombin time, partial thromboplastin time, and buccal mucosal bleeding time were unremarkable; activated clotting time, plasma von Willebrand factor concentration, results of platelet function testing, and plasma factor VII, VIII, IX, X, XI, and XII concentrations were considered normal. At this evaluation, clinicopathologic analyses revealed mild regenerative anemia that progressed over a 4-day period to moderate regenerative anemia and acute inflammation with panhypoproteinemia. Abdominal ultrasonography revealed a large mass (suspected to be a hematoma) near the urinary bladder. Rotational thromboelastometry revealed that clotting times were within reference limits, with abnormal clot formation times and clot firmness. The result of a factor XIII (FXIII) clot solubility assay confirmed FXIII deficiency. Treatment and Outcome—The dog’s bleeding diathesis resolved with inpatient care and IV fluid therapy, although plasma transfusions had been required at previous evaluations. Seven months after discharge from the hospital, the dog continued to do well clinically, although it had several additional episodes of excessive bleeding. Clinical Relevance—To the authors’ knowledge, this is the first reported case of congenital FXIII deficiency in a dog. In addition to more common inherited coagulopathies, FXIII deficiency should be a differential diagnosis for dogs with episodes of excessive bleeding and apparently normal results of standard coagulation tests. (J Am Vet Med Assoc 2014;245:1147–1152)
A
5-year-old 10.2-kg (22.4-lb) castrated male Toy Poodle cross was evaluated at the Veterinary Medical Centre at the Western College of Veterinary Medicine on an emergency basis because of lethargy and decreased appetite of 4 days’ duration and suspected abdominal bleeding. The dog was administered IV fluid therapy (lactated Ringer’s solution; 15 mL/h) and cefazolin (22 mg/kg [10 mg/lb], IV, q 8 h) by the referring veterinarian starting 2 days prior to the evaluation. Two brief abdominal ultrasonographic examinations performed by the referring veterinarian 2 days and 1 day prior to this evaluation revealed accumulating free fluid. Abnormal hematologic findings included mild regenerative anemia (RBC count, 5.08 X 1012 RBCs/L [reference range, 5.20 X 1012 RBCs/L to 8.20 X 1012 RBCs/L]; Hct, 0.335 L/L [reference range, 0.365 to 0.573 L/L]; and proportion of reticulocytes, 2.5%) and evidence of acute inflammation (WBC count, 22.1 X 109 WBCs/L From the Departments of Small Animal Clinical Sciences (Kong, Snead, Dhumeaux) and Pathology (Burgess), Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada. Dr. Kong’s present address is Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PE C1A 4P3, Canada. Dr. Dhumeaux’s present address is Pride Veterinary Centre, Riverside Rd, Pride Park, Derby DE24 8HX, England. The authors thank Dr. Robert Devaraj for assistance with the factor XIII clot solubility assay. Address correspondence to Dr. Kong ([email protected]). JAVMA, Vol 245, No. 10, November 15, 2014
ABBREVIATIONS aPTT CFT FXIII MCF PT
Activated partial thromboplastin time Clot formation time Factor XIII Maximum clot firmness Prothrombin time
[reference range, 4.80 X 109 WBCs/L to 13.9 X 109 WBCs/L]; neutrophil count, 16.796 X 109 neutrophils/L [reference range, 3.0 X 109 neutrophils/L to 10 X 109 neutrophils/L]; and band neutrophil count, 2.431 X 109 band neutrophils/L [reference range, 0.0 X 109 band neutrophils/L to 0.1 X 109 band neutrophils/L]; slight toxic change detected). Panhypoproteinemia (total protein concentration, 44 g/L [reference range, 55 to 71 g/L]; albumin concentration, 29 g/L [reference range, 32 to 42 g/L]; and globulin concentration, 15 g/L [reference range, 20 to 34 g/L]) was identified via serum biochemical analysis. The dog subsequently developed hematuria and was referred to the Veterinary Medical Centre for a possible blood transfusion. The dog had no history of trauma prior to evaluation by the referring veterinarian on this occasion, but pertinent past medical history included several episodes of excessive bleeding associated with trauma or surgical procedures. At 6 months of age, scrotal hemorrhage occurred after the dog was neutered. The surgical Scientific Reports
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incision was reopened multiple times over the following 5 days to remove blood clots, and a blood transfusion was required 6 days after neutering. At that time, the dog’s platelet count was estimated as normal (automated count, 111 X 109 platelets/L; reference range, 200 X 109 platelets/L to 900 X 109 platelets/L) with platelet clumps on blood smear examination. Plasma concentration of von Willebrand factor antigen was within reference range (76%; reference range, 45% to 180%). The PT was not prolonged (7.1 seconds; reference range, 7.5 to 9.9 seconds), and the aPTT, although mildly prolonged (13.9 seconds; reference range, 9.6 to 13.8 seconds), was not deemed sufficiently high to be responsible for the amount of hemorrhage seen. At 9 months of age, the dog was evaluated by the Veterinary Medical Centre ophthalmology service; a presumptive diagnosis of congenital glaucoma that was nonresponsive to medical management necessitated left eye enucleation. Results of preoperative hematologic and serum biochemical analysis and buccal mucosal bleeding time (< 4 minutes; reference range,1 1.7 to 4.2 minutes) were apparently normal. The dog underwent blood typing and cross-matching prior to surgery. Minimal hemorrhage occurred during surgery, but moderate oozing of blood was noted from the enucleation incision after surgery. The dog’s PCV was 41% (reference range, 36.5% to 57.3%). Given that its condition appeared stable, the dog was discharged from the hospital. However, the dog was reevaluated that evening because of excessive bleeding from the surgical site. The PT (7.7 seconds), aPTT (13.3 seconds), and activated clotting time (< 120 seconds; reference range,2 60 to 125 seconds) were all within reference limits. The dog’s PCV had decreased to 25%; hence, the dog was administered diphenhydramine (2 mg/kg [0.9 mg/lb], IM) and a transfusion of stored whole blood (110 mL). Histologic evaluation of the enucleated eye confirmed congenital glaucoma. Two weeks after the enucleation, the dog was evaluated at a private veterinary clinic because of signs of pain on opening its mouth and signs of depression; palpation of the left side of the face elicited signs of pain. The dog was sedated, and an examination of the oral cavity was performed. The examination revealed a swelling at the left caudal aspect of the mouth, which, on aspiration, was found to contain blood. The dog was again referred to the Veterinary Medical Centre, but no treatment was given because the mass was resolving. The mass was attributed to hemorrhage secondary to a hitherto undiagnosed coagulopathy. A platelet function testa was performed, and results were considered normal (96 seconds; reference range,3 48 to 105 seconds). At 2 years of age, the dog was evaluated at another private veterinary clinic because of a bite wound to the abdomen. The dog developed a subcutaneous hematoma near its right quadriceps femoris muscle, along with extensive bruising on the ventral aspect of the abdomen and in the inguinal region, and was referred to the Veterinary Medical Centre for evaluation of excessive bleeding that resulted in moderate regenerative anemia (RBC count, 3.8 X 1012 RBCs/L; Hct, 0.259 L/L; and proportion of reticulocytes, 6.1%). The platelet count, PT, aPTT, and buccal mucosal bleeding time were again within reference ranges. To verify the findings of the 1148
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screening test at our laboratory and to rule out a mild factor deficiency not detected by the PT and aPTT testing, screening coagulation tests were repeated, and specific factor assay testing was performed through the Cornell University Animal Health Diagnostic Center. These analyses revealed no abnormalities, as follows: aPTT, 12.1 seconds (reference range, 10 to 17 seconds); PT, 14.6 seconds (reference range, 11 to 16 seconds); thrombin clotting time, 6.0 seconds (reference range, 5 to 9 seconds); plasma von Willebrand factor antigen concentration, 143% (reference range, 70% to 180%); plasma factor VII concentration, 118% (reference range, 50% to 150%); plasma factor VIII concentration, 87.5% (reference range, 50% to 200%); plasma factor IX concentration, 86% (reference range, 50% to 150%); plasma factor X concentration, 87% (reference range, 80% to 175%); plasma factor XI concentration, 97% (reference range, 60% to 150%); and plasma factor XII concentration, 92% (reference range, 60% to 150%). Given the undefined nature of the dog’s hemostatic defect, the owners were told to expect further bleeding episodes following any type of trauma and that administration of fresh frozen plasma would be necessary prior to any surgical procedure. Differential diagnoses for the dog’s bleeding disorder included a deficiency in antifibrinolytic proteins, a rare platelet function defect (eg, Scott syndrome), or a deficiency in FXIII; however, the owners declined further investigation. At 3 years of age, the dog was again referred to the Veterinary Medical Centre because of a bite wound to its right ear that developed into a severe aural hematoma. During the 3 days preceding referral, the dog’s PCV had decreased from 45.5% to 29.2%, and its platelet count decreased from 275 X 109 platelets/L to 48 X 109 platelets/L (reference range, 200 X 109 platelets/L to 900 X 109 platelets/L). The PT and aPTT were again within reference ranges. The hematoma eventually resolved with repeated application of pressure bandages over a 4-day period of hospitalization. Although FXIII deficiency testing was recommended at this time, the owners failed to bring the dog back for the necessary follow-up. At the current evaluation, the dog was lethargic, and signs of pain were elicited during abdominal palpation. There were mild areas of ecchymotic hemorrhage on the right side of the abdominal wall. Abdominal ultrasonography revealed subcutaneous edema, moderate peritoneal effusion, and a hypoechoic mass near the urinary bladder. The dog was hospitalized. During a period of 4 days, the dog’s initial mild regenerative anemia progressed to moderate regenerative anemia (RBC count, 3.46 X 1012 RBCs/L; Hct, 0.239 L/L; and proportion of reticulocytes, 4.4%). The dog also developed thrombocytopenia (platelet count decreased from estimated normal to between 25 X 109 platelets/L and 100 X 109 platelets/L) during that period. The mass near the urinary bladder was suspected to be a hematoma or an intra-abdominal neoplasm on the basis of findings of repeated abdominal ultrasonographic examinations. Collection of aspiration or biopsy specimens of the mass could not be performed because of the dog’s coagulopathy and current thrombocytopenia. Rotational thromboelastometryb and an FXIII clot solubility assay were performed to further investigate JAVMA, Vol 245, No. 10, November 15, 2014
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the cause of the dog’s underlying coagulopathy. Thromboelastometry is an in vitro diagnostic technique that can continuously record changes in the viscoelastic properties of whole blood during clotting and fibrinolysis. It has clinical applications for diagnosis of hypercoagulable states, platelet function disorders, and defects in fibrin formation and fibrinolysis via a series of assays: an extrinsic pathway assay with tissue factor reagent (Figure 1), an intrinsic pathway assay with ellagic acid reagent (Figure 2), and a fibrinolysis assay with cytochalasin D in DMSO solution and 0.2M CaCl2 in HEPES buffer (pH, 7.4; Figure 3). Although the dog had normal clotting times (measured in seconds from clot initiation to a clot amplitude of 2 mm) for thromboelastometry assays evaluating the extrinsic (43 seconds; reference range, 29 to 75 seconds) and intrinsic (139 seconds; reference range,4 129 to 200 seconds) pathways, CFT (measured in seconds from a clot amplitude of 2 to 20 mm) could not be determined in the extrinsic pathway assay (reference range,4 66 to 186 seconds) because the clot did not reach an amplitude of 20 mm and was delayed in the intrinsic pathway assay (744 seconds; reference range,4 48 to 237 seconds). The MCF (maximum clot amplitude) was decreased for all assays (extrinsic pathway assay, 19 mm [reference range,4 46 to 63 mm]; intrinsic pathway assay, 22 mm [reference range,4 45 to 64 mm]; and fibrinolysis assay, 4 mm [reference range,5 6 to 26 mm]). Assessment of the rotational thromboelastometry tracings revealed a small clot with a decreased slope of the line delimiting the α angle, indicating slow clot formation. A citrated blood sample from this dog along with a sample from an ageand breed-matched clinically normal dog was sent to Regina General Hospital to undergo an FXIII clot solubility assay. The clot solubility assay determines the interval to lysis of a stabilized clot after addition of either a 1% monochloroacetic acid or 5M urea solution; in blood samples obtained from individuals with an FXIII deficiency, clot lysis time is shortened (ie, < 24 hours) owing to poor cross-linking of the fibrin clot. Results of this test were abnormal (clot dissolution occurred within 24 hours following incubation) for the sample from the dog of this report and were normal (the clot remained stable after 24 hours of incubation) for the sample from the control dog. The dog was treated IV with isotonic electrolyte solutionc supplemented with
Figure 1—Extrinsic pathway thromboelastogram obtained for a 5-year-old Toy Poodle cross that was evaluated because of lethargy and decreased appetite of 4 days’ duration and suspected abdominal bleeding. The dog had been evaluated on 4 other occasions because of episodes of excessive bleeding associated with trauma or surgical procedures. Specific coagulation factor testing subsequently confirmed that the dog had an FXIII deficiency. The clotting time (measured in seconds from clot initiation to a clot amplitude of 2 mm, end point demarcated by the change from dark gray to light gray) is within reference limits (43 seconds; reference range, 29 to 75 seconds), but CFT (measured in seconds from a clot amplitude of 2 to 20 mm) could not be determined because the clot amplitude never reached 20 mm. The slope of the line represents the α angle (the rate of clot formation), which was low (26°; reference range, 58° to 76°). The MCF (maximum clot amplitude) is also decreased (19 mm; reference range, 46 to 63 mm). Dashed lines represent the lower reference limit for MCF.
Figure 2—Intrinsic pathway thromboelastogram obtained for the same dog as in Figure 1. The clotting time (end point demarcated by the change from dark gray to gray) is within reference limits (139 seconds; reference range, 129 to 200 seconds), but CFT (end point demarcated by the change from gray to light gray) is markedly prolonged (744 seconds; reference range, 48 to 237 seconds). The slope of the line represents the α angle, which is low (36°; reference range, 52° to 78°). The MCF is decreased (22 mm; reference range, 45 to 64 mm). Dashed lines represent the lower reference limit for MCF.
Figure 3—Fibrinolysis thromboelastogram obtained for the same dog as in Figure 1. The MCF is low (4 mm; reference range, 6 to 26 mm), and visually, the clot amplitude appears uniformly decreased. Dashed lines represent the lower reference limit for MCF. Scientific Reports
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20 mEq of KCl/L (26 mL/h) from the day of admission until discharge. The dog was discharged from the hospital 5 days after evaluation. The owners were instructed to return the dog for follow-up ultrasonography in 1 month. Two months later, the dog was evaluated by its regular veterinarian for routine vaccination. Findings of follow-up ultrasonography of the abdomen performed by the referring veterinarian at that time were unremarkable. Following vaccination, the dog developed a large subcutaneous hematoma leading to non–weightbearing lameness, which subsequently resolved. Five months after vaccination, the dog jumped out of a car, resulting in severe abdominal hemorrhage that limited its ability to walk; ambulation was assisted with sling support, and the dog did not require hospitalization. The injury resolved. At the time of the injury, hematologic analysis revealed moderate anemia (RBC, 3.47 X 1012 RBCs/L [reference range, 5.50 X 1012 RBCs/L to 8.50 X 1012 RBCs/L]; Hct, 0.223 L/L [reference range, 0.370 to 0.550 L/L]). An ultrasonographic examination performed a week later confirmed resolution of the bleeding. Discussion Factor XIII deficiency is a coagulopathy that is rare in people6 and, to the authors’ knowledge, has not been previously described for domestic animals. Factor XIII is involved in stabilizing the initial fibrin clot formed during secondary hemostasis. Clinical signs of congenital FXIII deficiency in people include umbilical stump bleeding; hemarthrosis; poor wound healing; bleeding after surgery, minor trauma, or strenuous exercise; recurrent miscarriages; and intracranial bleeding.7,8 The latter is a major cause of death and disability in affected humans. This case report is the first to describe congenital FXIII deficiency in a dog with multiple episodes of severe bleeding starting from a young age. Factor XIII is the final coagulation factor in the coagulation cascade and because of its function is referred to as the fibrin-clot stabilizing factor. It circulates in plasma as a tetramer of 2 catalytic A subunits and 2 carrier B subunits (A2B2). Thrombin, together with Ca2+, fibrin, and fibrinogen, activates FXIII by cleavage of the activation peptide from the A subunit.9 The final step in activation, which involves dissociation of the A subunits from the B subunits, is also greatly accelerated by Ca2+ and fibrin. Activated FXIII then covalently cross-links fibrin polymers, converting them from loose polymers into an organized clot.9 Through this process, the stable fibrin clot is able to firmly adhere to the underlying wound so that it is not easily dislodged by shear stress. In addition, activated FXIII incorporates antifibrinolytic proteins such as α2-antiplasmin into the clot to help prevent premature degradation of the clot by the fibrinolytic system.9 The recurrent episodes of excessive hemorrhage over a period of several years in the dog of this report were highly suggestive of an inherited coagulopathy; however, pedigree information for the dog’s sire and dam was not available, and this dog was the only puppy born alive in that litter. Commonly used screening tests 1150
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ruled out well-known coagulopathies early, leaving only a few remaining possible differential diagnoses (rare platelet function defect; a deficiency in plasminogen activator inhibitor-1, α2-antiplasmin, or thrombin-activated fibrinolysis inhibitor [the latter leading to a hyperfibrinolytic state]; and an FXIII deficiency). A thrombopathy was less likely on the basis of the dog’s apparently normal result on platelet function testing,a which has a high reported sensitivity (95.7%) and specificity (100%) with use of the ADP-collagen cartridgea for detection of a platelet function defect in dogs; however, because the platelet function testa may not consistently detect milder forms of platelet dysfunction and certain platelet disorders (storage pool disease or Scott syndrome),11,12 a platelet function abnormality was not definitively ruled out on the basis of this result. The platelet function testa can also be used to detect abnormalities in von Willebrand factor function; normal test results for this dog made a von Willebrand factor dysfunction unlikely.13 Rotational thromboelastometry findings also conclusively ruled out both a thrombocytopathia and a fibrinolytic system abnormality, and the clot solubility test confirmed the dog’s FXIII deficiency. On the basis of a search of the veterinary medical literature, this is the first reported case of congenital FXIII deficiency in a dog, to the authors’ knowledge. Congenital FXIII deficiency in humans has been reported,14 and knockout mice have been bred specifically for an FXIII deficiency.15 In people, it is considered a rare coagulation disorder that has a much lower incidence than either hemophilia A or B6 and most commonly results from a deficiency in the A subunits (type 2 defect), although it can also result from a lack of B subunits (type 1 defect).9 Patients with congenital FXIII deficiency have a severe bleeding diathesis, typically apparent after trauma. Bleeding after a traumatic event will often be delayed because the blood clots formed are loose and therefore contribute to rebleeding when not stabilized. This diathesis and delay in onset of bleeding were evident in the dog described in the present report, wherein all but 1 incidence of abnormal bleeding were subsequent to surgical or accidental trauma and bleeding was often delayed following surgical procedures. In addition to its hemostatic role, FXIII is also important for maintenance of pregnancy, for wound healing and tissue repair, and for angiogenesis.16 Recurrent miscarriages are common in affected women.7 In affected people, wound healing occurs extremely slowly; thus, wounds continue to bleed for a prolonged period (as long as several weeks) despite surgical intervention or compressive bandages, similar to the clinical features of the case described in this report. Diagnosis of FXIII deficiency is challenging because the most commonly used results of screening tests for primary and secondary hemostatic diatheses are expected to be normal.17 Tests for secondary hemostasis (PT and aPTT) detect only the appearance of polymerized fibrin but not its stabilization by FXIII. In the dog of this report, the repeatedly unremarkable PT, aPTT, and thrombin clotting time made abnormalities in factors I, II, V, VII, VIII, IX, X, XI, XII, prekallikrein, and high-molecular-weight kininogen unlikely,18 although a mild factor deficiency could not be conclusively ruled JAVMA, Vol 245, No. 10, November 15, 2014
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deficiency in the case described in this report because the data can reflect abnormalities with fibrin formation and cross-linking. Thromboelastography incorporates different assays that evaluate the intrinsic or contact pathway (analogous to aPTT assessment), the extrinsic or tissue factor pathway (analogous to PT assessment), and fibrinolysis (by irreversibly inhibiting platelets with cytochalasin D to eliminate the platelet contribution to clot formation).21 Thromboelastometry, a modification of thromboelastography, was used to test the patient in this report. Clotting time is primarily a function of coagulation factor concentrations, whereas CFT and MCF rely more on platelet function and fibrin formation and cross-linking.22 Normal clotting time, with delayed CFT and decreased MCF, as detected in the dog of this report, was consistent with either an FXIII deficiency or platelet abnormality. Thrombocytopenia at the time of testing could have influenced these results by falsely increasing CFT and decreasing MCF as determined by the intrinsic and extrinsic pathway assays; however, the fibrinolysis assay removes platelet contribution to clotting, and concurrent abnormal MCF results determined by the fibrinolysis assay ruled out thrombocytopenia (along with other platelet abnormalities) at the time of testing as a sole cause for abnormal CFT and MCF revealed by the intrinsic and extrinsic pathway assays. Thromboelastography has been validated as a specific and sensitive test for detection of FXIII deficiency in people.23 Thromboelastometry, as a modification of thromboelastography, is assumed to have similar sensitivity and specificity, and it was the only test other than the clot solubility test that yielded abnormal findings in this dog; therefore, thromboelastometry should be considered a useful diagnostic tool for investigating a coagulopathy where the underlying cause is not evident on the basis of standard screening test results. Treatment of humans with FXIII deficiency traditionally consists of cryoprecipitate or fresh frozen plasma transfusions administered every 4 to 6 weeks. More recently, a new treatment that uses plasma-derived pasteurized FXIII concentrate has been available.9 The only treatment option currently available for veterinary patients would be frequent administration of either cryoprecipitate or fresh frozen plasma given the lack of species-specific FXIII concentrate. Prevention of bleeding by means of intermittent administration of cryoprecipitate has been attempted in humans,9 but this may not be financially viable for many veterinary clients. Gene therapy has been explored as a possible treatment option in dogs with hemophilia B (factor IX deficiency)24 or hemophilia A (factor VIII deficiency)25 and may represent an area for future research. In the case described in this report, treatment included advising the owners to minimize or prevent any traumatic events and providing transfusions to stabilize the dog after episodes of bleeding. Factor XIII deficiency may be considered as a differential diagnosis in dogs with a coagulopathy that is not detected by standard coagulation screening tests. A thorough evaluation for more common inherited coagulopathies (von Willebrand disease, hemophilia A, and hemophilia B) should be performed before considering FXIII testing. Platelet function testing and rotational thromboelastometry may be helpful diagnostic Scientific Reports
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out prior to specific factor testing. Although PT and aPTT are reliably used to detect severe deficiencies in clotting factors associated with secondary hemostasis, both tests have relatively low sensitivity (30%) for detection of mild factor deficiencies, and such sensitivities can vary depending on the deficient factor and the reagent used in the tests.19,20 Possible deficiencies in factors VII through XII were conclusively ruled out through factor testing for the dog of this report. In addition, patients with an FXIII deficiency will have a platelet count, platelet function test results, and plasma von Willebrand factor antigen concentration that are all within reference limits, as seen in the dog of this report, thereby ruling out common primary hemostatic disorders. Although the dog was thrombocytopenic during 2 episodes of bleeding, this was likely a result of platelet consumption during excessive hemorrhage. Platelet count was within reference range at most evaluations, ruling out thrombocytopenia as a cause of the dog’s excessive bleeding. A clot solubility test has been traditionally used to diagnose an FXIII deficiency in people.9 For this test, a plasma sample from an affected patient is incubated with a buffer of calcium and thrombin to promote clot stabilization. The clot is then suspended in a freshly prepared solution of either 1% monochloroacetic acid or a 5M urea solution and left undisturbed at 37°C for 24 hours. In a patient with normal FXIII concentration, the clot remains stable after 24 hours. Clot lysis occurs rapidly (typically within hours) when an FXIII deficiency exists because the fibrin clot formed is poorly crosslinked and dissolves more quickly.9 Controls (blood samples from apparently normal individuals) must also be run when the test is performed, and considering that the test is manual, it must be performed in duplicate. Owing to the semiquantitative nature of this assay, only severe FXIII deficiencies (activity of FXIII, < 1% of activity in a clinically normal individual) may be detected, which can delay diagnoses in some humans with less severe deficiencies.8 Even the addition of a small amount of plasma from a healthy individual to the test system will elevate FXIII activity to 1% to 3% of that expected in clinically normal individuals and render the clot insoluble. Hence, this test should not be run if plasma has been administered to the patient within the preceding few weeks. Despite this shortcoming, the clot solubility test is still used by many laboratories for the diagnosis of an FXIII deficiency in humans because of its simplicity and the lack of readily available and more quantitative diagnostic tests. Confirmation of the diagnosis, especially for mild or moderate deficiencies of FXIII, is ideally provided by use of a more quantitative test that measures FXIII activity or antigen concentration.8 As part of the diagnosis of FXIII deficiency, PCR testing has been used in to identify the specific type of mutation (A or B subunit) responsible. Because there are no dog-specific assays for determining plasma FXIII activity or antigen concentration, the clot solubility test was used to establish the diagnosis for the dog of this report. Testing for a specific subunit deficiency in this dog was not done for financial and practical reasons. Results of rotational thromboelastometry proved useful in helping to support the diagnosis of an FXIII
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tools, but specific testing for an FXIII deficiency in dogs currently relies on an abnormal clot solubility test. No highly practical or affordable treatment options are currently available for veterinary patients with FXIII deficiency, but prophylactic treatment with fresh frozen plasma transfusions should be provided before any elective or emergency surgical procedure, and owners should be warned that bleeding after trauma, even minor trauma associated with vaccination, is possible. a. b. c.
PFA-100 collagen/ADP cartridge, Siemens, Malvern, Pa. ROTEM, Pentapharm, Munich, Germany. Normosol-R, Hospira, Lake Forest, Ill.
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11. Harrison P, Mackie IJ, Joseph J, et al. Performance of the platelet function analyser PFA-100 in testing abnormalities of primary haemostasis. Blood Coagul Fibrinolysis 1999;10:25–31. 12. Brooks MB, Randolph J, Warner K, et al. Evaluation of platelet function screening tests to detect platelet procoagulant deficiency in dogs with Scott syndrome. Vet Clin Pathol 2009;38:306– 315. 13. Favaloro EJ. The utility of the PFA-100 in the identification of von Willebrand disease: a concise review. Semin Thromb Hemost 2006;32:537–545. 14. Burrows RF, Ray JG, Burrows EA. Bleeding risk and reproductive capacity among patients with factor XIII deficiency: a case presentation and review of the literature. Obstet Gynecol Surv 2000;55:103–108. 15. Lauer P, Metzner HJ, Zettlmeissl G, et al. Targeted inactivation of the mouse locus encoding coagulation factor XIII-A: hemostatic abnormalities in mutant mice and characterization of the coagulation deficit. Thromb Haemost 2002;88:967–974. 16. Schroeder V, Kohler HP. New developments in the area of factor XIII. J Thromb Haemost 2013;11:234–244. 17. Bolton-Maggs PH. The rare inherited coagulation disorders. Pediatr Blood Cancer 2013;60(suppl 1):S37–S40. 18. Triplett DA. Coagulation and bleeding disorders: review and update. Clin Chem 2000;46:1260–1269. 19. Mischke R. Activated partial thromboplastin time as a screening test of minor or moderate coagulation factor deficiencies for canine plasma: sensitivity of different commercial reagents. J Vet Diagn Invest 2000;12:433–437. 20. Mischke R, Diedrich M, Nolte I. Sensitivity of different prothrombin time assays to factor VII deficiency in canine plasma. Vet J 2003;166:79–85. 21. Velik-Salchner C, Schnürer C, Fries D, et al. Normal values for thrombelastography (ROTEM) and selected coagulation parameters in porcine blood. Thromb Res 2006;117:597–602. 22. Smith SA, McMichael MA, Gilor S, et al. Correlation of hematocrit, platelet concentration, and plasma coagulation factors with results of thromboelastometry in canine whole blood samples. Am J Vet Res 2012;73:789–798. 23. Schroeder V, Chatterjee T, Kohler H. Influence of blood coagulation factor XIII and FXIII Val34Leu on plasma clot formation measured by thrombelastography. Thromb Res 2001;104:467–474. 24. Kay MA, Rothenberg S, Landen CN, et al. In vivo gene therapy of hemophilia B: sustained partial correction in factor IX-deficient dogs. Science 1993;262:117–119. 25. Connelly S, Mount J, Mauser A, et al. Complete short-term correction of canine hemophilia A by in vivo gene therapy. Blood 1996;88:3846–3853.
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