Ind J Clin Biochem DOI 10.1007/s12291-013-0368-2
CASE REPORT
Spurious Hyperphosphatemia in a Case of Multiple Myeloma Sutirtha Chakraborty • Susruta Sen • Debkishore Gupta • Sidhartha Sankar Ghosh Prasad Sawant • Mandrita Das
•
Received: 12 June 2013 / Accepted: 22 July 2013 Ó Association of Clinical Biochemists of India 2013
Abstract A 50 year old male was admitted in our hospital with anemia and impaired renal function. He was subsequently found to have extremely elevated serum phosphate level (24 mg/dL, reference interval: 2.5–4.5 mg/dL) with normal serum calcium when assayed on a Beckman Coulter AU 480Ò analyser. Clinico-biochemical discrepancy led to the suspicion of spurious hyperphosphatemia. Serum total protein was grossly elevated with gross reversal of albumin to globulin ratio. Serum electrophoresis revealed a large M band and was confirmed as Ig G-Kappa type on immunofixation. Subsequently a bone marrow aspiration biopsy confirmed the diagnosis of multiple myeloma. The patient serum was then reassayed for phosphate on a VitrosÒ 250 Dry Chemistry platform and the result was within normal reference interval. Paraproteinemias are a common cause of
S. Chakraborty (&) S. S. Ghosh Department of Biochemistry, Peerless Hospital & B K Roy Research Centre, Kolkata 700094, West Bengal, India e-mail: [email protected]; [email protected] S. S. Ghosh e-mail: [email protected] S. Sen M. Das Department of Biochemistry, Calcutta Medical Research Institute, Kolkata, India e-mail: [email protected] D. Gupta Department of Microbiology, Peerless Hospital & B K Roy Research Centre, Kolkata, India e-mail: [email protected] P. Sawant Mumbai, India e-mail: [email protected]
analytical interference in clinical biochemistry laboratories and as multilayered film technology platforms like VitrosÒ assay most routine analytes on a protein free filtrate they are unaffected by paraprotein interference. Clinically discordant patient results should always be interpreted keeping such interferences in mind. Keywords Hyperphosphatemia Paraprotein Multiple myeloma Interference
Case Summary A 50 year old male patient presented to Peerless Hospital OPD with progressively increasing generalised weakness and shortness of breath for the last 4 months. He was subsequently admitted in our hospital for diagnostic further evaluation. On admission his serum creatinine was 3.15 mg/dL [reference interval (RI): 0.6–1.4 mg/dL], Urea was 98 mg/dL (RI 15–45 mg/dL) and the complete hemogram showed a haemoglobin of 7.8 g/dL (RI 12–15 g/dL) with the peripheral blood smear revealing a normocytic normochromic type of anemia. He was diabetic and was well controlled using oral medications. His blood pressure was normal. His urine protein was 2? on dipstick but was negative for glucose, ketones and occult blood. His serum electrolytes were within normal limits. Due to the presence of impaired renal function, serum calcium and phosphate were ordered. The calcium was 10.1 mg/dL (RI: 8.5–10.5 mg/dL) and serum phosphate was 24 mg/dL (RI: 2.5–4.5 mg/dL). Serum phosphate was rechecked on a repeat sample and the results were similar. Intact PTH was also done and found to be within the normal limits (62 pg/mL, RI: 15–65 pg/mL). Chest X ray and USG-whole abdomen were unremarkable.
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Ind J Clin Biochem
Discussion Such an extremely elevated serum phosphate level is almost impossible physiologically and to evaluate the cause we measured serum PTH in our patient. Grossly elevated phosphate might occur in cases of phosphate poisoning and in such patients there is a sharp elevation of the PTH level as a result of the compensatory mechanism. As the PTH was normal this was likely a spurious elevation in phosphate also known as pseudohyperphosphatemia. Iatrogenic hyperphosphatemia may occur in patients with excessive oral or intravenous phosphate administration or overuse of phosphate rich enemas [1]. In our case the clinical history of the patient was not suggestive of any phosphate use. Lipemia, icterus, hemolysis (LIH) are well known to interfere in the analytical process but paraproteinemia is also a common cause of analytical interference leading to spuriously elevated phosphate [2]. Considering this possibility, we reflectively measured the total serum protein and albumin and calculated the albumin-to-globulin ratio. The total protein was 11.4 g/dL (RI 6.6–8.0 g/dL) and the albumin was 2.3 g/dL (RI 3.5–5.0 g/dL).This prompted us to perform a serum electrophoresis which revealed a band of restricted mobility in the gamma globulin region. The patient sample was then assayed for phosphate by serial dilutions. There was complete lack of linearity in the phosphate results suggesting an analytical interference (Table 1). This issue was discussed with the treating physician and the diagnosis of multiple myeloma was confirmed by bone marrow aspiration biopsy. An X-ray of the skull revealed a punched out lytic lesion typical of multiple myeloma. Immunofixation was done which showed an IgG kappa monoclonal M-spike. The serum IgG was 11,500 mg/dL (RI 450–1,500 mg/dL) while the other immunoglobulins were within the RIs. Spurious hyperphosphatemia in patients with paraproteinemias like multiple myeloma, Waldenstro¨m macroglobulinemia, and monoclonal gammopathy of undetermined significance are not uncommon. IgG kappa is well known to interfere with the phosphomolybdate principle used in the
Table 1 Showing the recovery of serum phosphate on the AU 480 analyser at various dilutions Dilution
Expected value (mg/dL)
Obtained value (mg/dL)
Conclusion It is interesting to note that spurious hypophosphatemia has also been reported as a result of paraprotein interference. [7] Clinically discordant biochemistry results should always be interpreted keeping such interferences in mind. Multilayered slide technology of VitrosÒ is possibly free from paraprotein interference and thus holds an important role in the biochemical analysis of patients with paraproteinemias specially multiple myeloma.
Recovery (%)
Direct
24
24
100
29
12
9.5
79.1
49
6
9.0
150
89
3
0.5
16.6
169
1.5
0.3
20
123
assay of serum phosphate on most automated chemistry analysers [3, 4]. Our phosphate result was obtained on a Beckman AU480 analyser but similar results were found on a Roche platform. All ‘‘wet’’ chemistry analysers will probably exhibit this interference in the phosphate assay. We then assayed the same sample for phosphate using a multilayered film technology based analyser (VitrosÒ 250, Ortho Clinical Diagnostics, USA) and the result was within the RI (4.1 mg/dL). The recovery obtained for phosphate on this analyser was excellent thus ruling out any possible interference. In multilayered film technology slides of VitrosÒ the uppermost layer contains BaSO4, which gives white background for reflectance. This layer is for optical diffusion, in addition it can retain high molecular weight substances (ultra-filtration step). But the spreading layer also fulfills another function by retaining dyes and opacifiers contained in the sample so that these cannot reach the reagent layer. This will largely prevent interference by serum chromogens/opacifiers thereby preventing interferences from hemolysis, icterus and lipemia. The material that has travelled through the spreading layer is a proteinfree filtrate, since proteins can also be retained. When determining proteins, a modified spreading layer is used that will not retain proteins. The BaSO4 spreading layer filters the protein (including paraprotein immunoglobulins) in serum and assays phosphate in a protein free filtrate [5, 6]. This prevents the positive interference of the IgG kappa monoclonal gammopathy. For labs which do not have a multilayered film technology based system, a serial dilution analysis of the suspected analyte could be performed. Lack of linearity or poor recovery on serial dilutions is an indirect indicator of potential interference.
References 1. Endres DB, Rude RK. Bone and mineral metabolism. In: Burtis CA, Ashwood ER, Bruns DE, editors. Tietz textbook of clinical chemistry and molecular diagnostics 4th ed. St. Louis: Elsevier; 2006. p. 1905–9.
Ind J Clin Biochem 2. Yang Y, Howanitz PJ, Howanitz JH, Gorfajn H, Wong K. Paraproteins are a common cause of interferences with automated chemistry methods. Arch Pathol Lab Med. 2008;132:217–23. 3. Hawkins RC. Pseudohyperphosphataemia in multiple myeloma. Ann Clin Biochem. 1991;28(Pt 3):226–8. 4. Larner AJ. Pseudohyperphosphatemia. Clin Biochem. 1995;28:391–3. 5. Sonntag O. Dry chemistry analysis with carrier-bound reagents. In: Van der Vliet PC, editor. Laboratory techniques in biochemistry and molecular biology Vol 25. London: Elsevier; 1993. p. 57–9.
6. Ortho Clinical Diagnostics. VITROS Chemistry Products PHOS Slides. Instructions for use [Product Insert]. Publication No. MP2–45, version 6.0. 7. Loghman-Adham M, Walton D, Iverius P, Deiss A, Knight JA, Cheung AK. Spurious hypophosphatemia in a patient with multiple myeloma. Am J Kidney Dis. 1997;30(4):571–5.
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CASE REPORT
Spurious Hyperphosphatemia in a Case of Multiple Myeloma Sutirtha Chakraborty • Susruta Sen • Debkishore Gupta • Sidhartha Sankar Ghosh Prasad Sawant • Mandrita Das
•
Received: 12 June 2013 / Accepted: 22 July 2013 Ó Association of Clinical Biochemists of India 2013
Abstract A 50 year old male was admitted in our hospital with anemia and impaired renal function. He was subsequently found to have extremely elevated serum phosphate level (24 mg/dL, reference interval: 2.5–4.5 mg/dL) with normal serum calcium when assayed on a Beckman Coulter AU 480Ò analyser. Clinico-biochemical discrepancy led to the suspicion of spurious hyperphosphatemia. Serum total protein was grossly elevated with gross reversal of albumin to globulin ratio. Serum electrophoresis revealed a large M band and was confirmed as Ig G-Kappa type on immunofixation. Subsequently a bone marrow aspiration biopsy confirmed the diagnosis of multiple myeloma. The patient serum was then reassayed for phosphate on a VitrosÒ 250 Dry Chemistry platform and the result was within normal reference interval. Paraproteinemias are a common cause of
S. Chakraborty (&) S. S. Ghosh Department of Biochemistry, Peerless Hospital & B K Roy Research Centre, Kolkata 700094, West Bengal, India e-mail: [email protected]; [email protected] S. S. Ghosh e-mail: [email protected] S. Sen M. Das Department of Biochemistry, Calcutta Medical Research Institute, Kolkata, India e-mail: [email protected] D. Gupta Department of Microbiology, Peerless Hospital & B K Roy Research Centre, Kolkata, India e-mail: [email protected] P. Sawant Mumbai, India e-mail: [email protected]
analytical interference in clinical biochemistry laboratories and as multilayered film technology platforms like VitrosÒ assay most routine analytes on a protein free filtrate they are unaffected by paraprotein interference. Clinically discordant patient results should always be interpreted keeping such interferences in mind. Keywords Hyperphosphatemia Paraprotein Multiple myeloma Interference
Case Summary A 50 year old male patient presented to Peerless Hospital OPD with progressively increasing generalised weakness and shortness of breath for the last 4 months. He was subsequently admitted in our hospital for diagnostic further evaluation. On admission his serum creatinine was 3.15 mg/dL [reference interval (RI): 0.6–1.4 mg/dL], Urea was 98 mg/dL (RI 15–45 mg/dL) and the complete hemogram showed a haemoglobin of 7.8 g/dL (RI 12–15 g/dL) with the peripheral blood smear revealing a normocytic normochromic type of anemia. He was diabetic and was well controlled using oral medications. His blood pressure was normal. His urine protein was 2? on dipstick but was negative for glucose, ketones and occult blood. His serum electrolytes were within normal limits. Due to the presence of impaired renal function, serum calcium and phosphate were ordered. The calcium was 10.1 mg/dL (RI: 8.5–10.5 mg/dL) and serum phosphate was 24 mg/dL (RI: 2.5–4.5 mg/dL). Serum phosphate was rechecked on a repeat sample and the results were similar. Intact PTH was also done and found to be within the normal limits (62 pg/mL, RI: 15–65 pg/mL). Chest X ray and USG-whole abdomen were unremarkable.
123
Ind J Clin Biochem
Discussion Such an extremely elevated serum phosphate level is almost impossible physiologically and to evaluate the cause we measured serum PTH in our patient. Grossly elevated phosphate might occur in cases of phosphate poisoning and in such patients there is a sharp elevation of the PTH level as a result of the compensatory mechanism. As the PTH was normal this was likely a spurious elevation in phosphate also known as pseudohyperphosphatemia. Iatrogenic hyperphosphatemia may occur in patients with excessive oral or intravenous phosphate administration or overuse of phosphate rich enemas [1]. In our case the clinical history of the patient was not suggestive of any phosphate use. Lipemia, icterus, hemolysis (LIH) are well known to interfere in the analytical process but paraproteinemia is also a common cause of analytical interference leading to spuriously elevated phosphate [2]. Considering this possibility, we reflectively measured the total serum protein and albumin and calculated the albumin-to-globulin ratio. The total protein was 11.4 g/dL (RI 6.6–8.0 g/dL) and the albumin was 2.3 g/dL (RI 3.5–5.0 g/dL).This prompted us to perform a serum electrophoresis which revealed a band of restricted mobility in the gamma globulin region. The patient sample was then assayed for phosphate by serial dilutions. There was complete lack of linearity in the phosphate results suggesting an analytical interference (Table 1). This issue was discussed with the treating physician and the diagnosis of multiple myeloma was confirmed by bone marrow aspiration biopsy. An X-ray of the skull revealed a punched out lytic lesion typical of multiple myeloma. Immunofixation was done which showed an IgG kappa monoclonal M-spike. The serum IgG was 11,500 mg/dL (RI 450–1,500 mg/dL) while the other immunoglobulins were within the RIs. Spurious hyperphosphatemia in patients with paraproteinemias like multiple myeloma, Waldenstro¨m macroglobulinemia, and monoclonal gammopathy of undetermined significance are not uncommon. IgG kappa is well known to interfere with the phosphomolybdate principle used in the
Table 1 Showing the recovery of serum phosphate on the AU 480 analyser at various dilutions Dilution
Expected value (mg/dL)
Obtained value (mg/dL)
Conclusion It is interesting to note that spurious hypophosphatemia has also been reported as a result of paraprotein interference. [7] Clinically discordant biochemistry results should always be interpreted keeping such interferences in mind. Multilayered slide technology of VitrosÒ is possibly free from paraprotein interference and thus holds an important role in the biochemical analysis of patients with paraproteinemias specially multiple myeloma.
Recovery (%)
Direct
24
24
100
29
12
9.5
79.1
49
6
9.0
150
89
3
0.5
16.6
169
1.5
0.3
20
123
assay of serum phosphate on most automated chemistry analysers [3, 4]. Our phosphate result was obtained on a Beckman AU480 analyser but similar results were found on a Roche platform. All ‘‘wet’’ chemistry analysers will probably exhibit this interference in the phosphate assay. We then assayed the same sample for phosphate using a multilayered film technology based analyser (VitrosÒ 250, Ortho Clinical Diagnostics, USA) and the result was within the RI (4.1 mg/dL). The recovery obtained for phosphate on this analyser was excellent thus ruling out any possible interference. In multilayered film technology slides of VitrosÒ the uppermost layer contains BaSO4, which gives white background for reflectance. This layer is for optical diffusion, in addition it can retain high molecular weight substances (ultra-filtration step). But the spreading layer also fulfills another function by retaining dyes and opacifiers contained in the sample so that these cannot reach the reagent layer. This will largely prevent interference by serum chromogens/opacifiers thereby preventing interferences from hemolysis, icterus and lipemia. The material that has travelled through the spreading layer is a proteinfree filtrate, since proteins can also be retained. When determining proteins, a modified spreading layer is used that will not retain proteins. The BaSO4 spreading layer filters the protein (including paraprotein immunoglobulins) in serum and assays phosphate in a protein free filtrate [5, 6]. This prevents the positive interference of the IgG kappa monoclonal gammopathy. For labs which do not have a multilayered film technology based system, a serial dilution analysis of the suspected analyte could be performed. Lack of linearity or poor recovery on serial dilutions is an indirect indicator of potential interference.
References 1. Endres DB, Rude RK. Bone and mineral metabolism. In: Burtis CA, Ashwood ER, Bruns DE, editors. Tietz textbook of clinical chemistry and molecular diagnostics 4th ed. St. Louis: Elsevier; 2006. p. 1905–9.
Ind J Clin Biochem 2. Yang Y, Howanitz PJ, Howanitz JH, Gorfajn H, Wong K. Paraproteins are a common cause of interferences with automated chemistry methods. Arch Pathol Lab Med. 2008;132:217–23. 3. Hawkins RC. Pseudohyperphosphataemia in multiple myeloma. Ann Clin Biochem. 1991;28(Pt 3):226–8. 4. Larner AJ. Pseudohyperphosphatemia. Clin Biochem. 1995;28:391–3. 5. Sonntag O. Dry chemistry analysis with carrier-bound reagents. In: Van der Vliet PC, editor. Laboratory techniques in biochemistry and molecular biology Vol 25. London: Elsevier; 1993. p. 57–9.
6. Ortho Clinical Diagnostics. VITROS Chemistry Products PHOS Slides. Instructions for use [Product Insert]. Publication No. MP2–45, version 6.0. 7. Loghman-Adham M, Walton D, Iverius P, Deiss A, Knight JA, Cheung AK. Spurious hypophosphatemia in a patient with multiple myeloma. Am J Kidney Dis. 1997;30(4):571–5.
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