REVIEW ARTICLE
Skin testing for inhalant allergy John A. Fornadley, MD, FAAOA
Background: Allergy is diagnosed by a combination of history, physical examination, and confirmatory testing. Modalities for testing include skin testing, in vitro assessment, and challenge testing of the conjunctiva or nasal mucosa. Challenge testing is primarily reserved for research. Methods: A review of the literature on skin testing methods for inhalant allergic rhinitis was performed. Results: Different forms of commonly used skin testing are available, including: individual prick; multiple prick; single, intradermal, and intradermal dilutional testing; and blended techniques. Each has inherent benefits and limitations. Conclusion: Skin testing remains a valid and in some cases superior means of identifying inhalant allergy. Skin-prick
S
pecific allergen testing in patients with a history and physical exam suspicious for inhalant allergy is indicated when knowledge of the patient’s sensitivities would lead to improvement in patient care. This testing can be performed by skin or laboratory (in vitro, specific immunoglobulin E [sIgE] blood testing) assessment. Typically, patients are tested with pertinent allergens based on history and geographic location because seasonal allergens in particular can vary by region. The results of such testing can provide important information, starting by identifying the presence or absence of allergy. This permits assessment of allergy as distiguished from other, nonallergic conditions, including nonallergic rhinitis with eosinophilia (NARES), irritant rhinitis, or vasomotor rhinitis, which can mimic or augment allergic disease. In addition, identification of specific allergens to which the patient is sensitive can allow therapy to be directed appropriately. Knowing the sen-
Clinical Associate Professor of Surgery, Division of Otolaryngology Penn State University, Hershey, PA Correspondence to: John A. Fornadley, MD, FAAOA, Penn State University, 1650 Brookline Drive, Hummelstown, PA 17036; e-mail: [email protected] Potential conflict of interest: J.A.F. is a stockholder, Glaxo SmithKline, Johnson and Johnson. Received: 30 June 2014; Revised: 3 July 2014; Accepted: 3 July 2014 DOI: 10.1002/alr.21393 View this article online at wileyonlinelibrary.com.
S41
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
testing and intradermal testing are the primary categories, although different formats exist for each. Caution must be taken to avoid creating a serious systemic reaction by injecting an injudicious amount of antigen into the skin, or in skin testing a patient whose medication profile puts them C 2014 ARS-AAOA, LLC. at increased risk.
Key Words: allergy testing; allergy test techniques; intradermal testing; modified quantitative testing; prick-puncture testing; skin testing How to Cite this Article: Fornadley JA. Skin testing for inhalant allergy. Int Forum Allergy Rhinol. 2014;4:S41–S45.
sitivities may guide environmental interventions, such as removing an animal from the environment, or selecting appropriate medications during the season when the specific allergen is present. Immunotherapy also requires knowledge of the specific allergen. Until the characterization of IgE in the 1960s and subsequent development of sIgE assays for this molecule, specific allergen testing could only be performed by direct challenge to the body. The primary organ for this testing has been the skin, although nasal, conjunctival, and bronchial routes of challenge have been described.1–3 The skin allows for a reasonably safe, reproducible, and visible region for evaluation of allergic response. Skin testing results can be semiquantitatively evaluated with less patient morbidity than would occur with testing the conjunctiva, nasal mucosa, or tracheobronchial tree. As the primary testing modality for the first 50 years of allergy therapy, skin testing has been studied extensively and refined. Even with development of in vitro assays for sIgE, skin testing remains an important, in many cases primary, means of testing individuals for allergy. There are several advantages of skin testing.4 The results are more rapid, with the skin reactivity read within 15 to 20 minutes, whereas with sIgE testing blood must be drawn in a laboratory and results typically take 1 to 2 days. Often, skin testing is a less costly modality than sIgE testing. The ability of the patient to experience firsthand the reaction
Fornadley
caused by the test antigens can be helpful in gaining the patient’s appreciation of the extent and severity of the disease process. Despite the prolonged experience with this modality, skin testing is subject to variability due to the technique, the risk of abnormally increased skin sensitivity, and the individual performing the test. There is also a subjective component to result interpretation.5 Skin testing techniques for inhalant allergens can be divided into epicutaneous (prick, prick-puncture) and intracutaneous (intradermal) techniques influence on outcomes. There are variations on each technique, and both modalities have a role in the correct identification of IgE-mediated allergy.
Epicutaneous testing
[IV]) needle against several commonly used lancet-type and solid (non-hypodermic) needles. The IV needle and metal lancets were judged to be the most satisfactory for reproducible testing results in comparison with other prick testing systems.7 In a nonsensitized patient, the epicutaneous prick test will not cause a local skin reaction. However, if an IgE-mediated sensitization exists, there will be release of histamine and development of a wheal (raised skin swelling reaction) from increased vascular permeability. Additionally, inflammatory mediators will create vasodilation, which results in a flare response (redness). Both the wheal and flare have been used to diagnose allergy.
Multiple-allergen prick-testing systems
Despite the advantages that have been identified for skin testing, the protective barrier function of the skin meant that it could not be tested in the same way as the antigen was applied directly to nasal mucosa, conjunctiva, or tracheobronchial tree. The presence of hair, oils, and keratinized epithelium limited the ability to identify all but the most dramatic sensitivities. Initial skin testing required placement of a small abrasion (“scratch testing”) to allow antigen access to a more sensitive, but still quite superficial, layer of skin. This method allowed successful identification of response to an allergen, but the variability in skin thickness, and technical difficulties creating a uniform scratch size and depth drastically limited the success of this technique. Therefore, scratch testing is no longer a recommended allergy testing modality.6 Derived from scratch testing, epicutaneous tests, also termed prick or prick-puncture, allow testing in the upper levels of skin. Concentrated antigen is delivered into the epicutaneous levels of skin by the use of a needle. This can be an intravenous (IV) type or a solid (non-hypodermic) needle. Skin-prick testing is generally more comfortable and safer than intradermal techniques that place antigen deeper into the skin. Because prick testing places allergen in a more superficial layer of skin, there is a decreased risk of provoking a systemic response in comparison to intradermal testing, in which the allergen in delivered deeper into the skin.
Individual prick testing causes minimal discomfort and is relatively inexpensive but can be time consuming and userdependent.8 In response to individual prick testing’s limitations, multiple simultaneous prick testing systems were developed that allow for placement of several allergens for testing with 1 application.9 The use of multiple-allergen skin-prick systems allows several antigens to be placed on the skin at 1 time. In addition to saving time, these devices more equally distribute the pressure exerted by each needle. Multiple test systems have multiple tines on each head; these tines can be dipped into a tray of wells containing different allergen extracts. The tines carry the allergen by capillary action. The benefit to these multiple-allergy prick tests includes more rapid testing and less technique-dependent influence on outcomes. There are different types of multiple-prick testing systems that vary in sensitivity and specificity. Dykewicz et al.10 reviewed 2 common multiple-prick testing devices, the Multi-test II (Lincoln Diagnostics, Decatur, IL) and the ComforTen (Allergy Laboratories, Oklahoma City, OK). The authors reported that the Multi-test II had lower coefficients of variability, greater wheal size, and higher sensitivity, but similar specificity to the ComfotTen. Overall, one should recognize that not all prick testing systems are the same and the results should be interpreted based upon the system used, because each system has specific instructions for interpretation included in the products based upon the wheal and flare responses elicited.
Individual prick testing
Intradermal testing
The back or volar surfaces of the arms provide ample skin surface for allergy testing and are of a relatively uniform thickness with less tendency to be hair-bearing. One drop of antigen concentrate for each individual antigen is placed on the skin. A single needle or lancet is passed through the antigen droplet and pricks the skin. The antigen is carried into the superficial skin area by the device at a reproducible quantity and depth. The current recommendation is to use 1 needle for each antigen.4 A variety of needles have been used for skin-prick testing. A recent review compared a hollow (hypodermic type
Although prick testing has been found to be quite specific, there may be concerns regarding a lower sensitivity (false negative). Injection of an antigen into the deeper layers of the skin can permit identification of a clinically significant allergen that was either not detected or is equivocally positive by skin-prick testing. Placement of an intradermal wheal places more antigen into deeper tissues that are beneath the epidermis, assuring that antigen comes in contact with vital (nonkeratinized) tissue. The disadvantage of intradermal testing is the risk of adverse reaction. Injecting concentrated antigen into more
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
S42
Skin testing for inhalant allergy
vascularized levels of the skin would risk a reaction that is unacceptably severe, including anaphylaxis.5 There are 2 methods available to clinicians to overcome this problem and harvest the useful information available from intradermal testing. The first method allowing safe injection of intradermal antigen is to perform the skin-prick testing first. If a positive response is observed, it will be clear that the patient is sensitive to the antigen, and no intradermal testing will be needed. On the contrary, the absence of a response on prick testing would alert the tester that an intradermal test wheal could be safely tolerated by the patient. This circumstance is most likely to arise when a patient’s history is markedly positive for an antigen, yet the prick testing does not confirm allergy. The intradermal test in this may identify allergic sensitization when skin-prick testing is negative. The clinical interpretation of a positive intradermal test after a negative skin-prick test is controversial. Some studies have demonstrated that a positive intradermal test after a negative skin-prick test does not correlate with allergy symptoms using either a pollen season11 or exposure to cats.12 Clinical interpretation is required based on knowledge of both the allergen and the patient. The second method that allows the safe use of intradermal injections is a serial dilution technique. In this technique, the concentrated antigen is diluted thousandsfold, until the antigen preparation is sufficiently dilute to pose minimal or no threat of anaphylaxis.13–15 Dilutions have been described using a 1:3, 1:5, or 1:10 calculations. King14 and King et al.15 summarized allergy testing using 1:5 dilutions of a commercial concentrate in the classic intradermal dilutional testing (IDT) method. Taking concentrated 1:20 wt/vol antigen and diluting this with saline, progressive dilutions of 1:100 (dilution #1), 1:500 (dilution #2), 1:2500 (dilution #3), etc. are created. A small quantity, approximately 0.04 mL, of the sixth 1:5 dilution (termed a #6 dilution) is injected intradermally to create a 4-mm wheal in the skin. This is observed for 10 to 15 minutes. In the nonallergic patient, due to skin laxity, the wheal grows slightly, to perhaps 5 mm, even in the absence of an allergic response. If there is minimal growth of this wheal, it is safe to move to a dilution of concentrate that is 5-fold more concentrated (the #5 dilution), and repeat the process. If the patient is allergic, the wheal will grow by at least 2 to 3 mm (approximately a 7-mm to 8-mm wheal). The choice of 5-fold dilution assures that the increase in antigen concentration is small enough that skin reaction should not exceed 2 to 3 mm. In the allergic patient, this series of skin reactions of progressively more concentrated intradermal tests, the skin reactions will show a wheal that grows by at least 2 mm to 7 mm or more (the “endpoint” wheal), and an additional wheal that also grows by at least 2 mm to 9 mm or more (the “confirming” wheal). The information identifies the patient as allergic, and the endpoint identifies the concentration of antigen at which immunotherapy can be safely initiated (Fig. 1). In the
S43
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
FIGURE 1. Intradermal dilutional testing positive whealing response.
case of a negative test to an allergen, as each more concentrated antigen solution is placed without a noted response, the test reaches a point where a sufficiently strong concentration of the antigen has been injected without reaction to assure that the individual is truly not allergic to the allergen being tested. Usually this would be the first or second dilution of the concentrate. The method of IDT (formerly called skin endpoint titration) has historically been considered as a “standalone” form of allergy testing that does not use skin-prick testing at all. Two aberrant skin responses to IDT have been described that one should be aware of: (1) the flash response, and (2) the plateau response.15 The flash response is one where there is an abnormally large wheal that develops with IDT after several negative wheals; when this occurs it is recommended to stop testing so that a systemic reaction is not provoked and to retest that allergen on another day. This flash response is thought to be due to cross-reactivity to foods ingested and/or environmental allergens in season at the time of testing. The plateau response occurs when there is a positive wheal (7 mm) that is followed by several wheals of the same size (several more 7-mm wheals) before a confirming wheal (9 mm) occurs. In this circumstance the first of the 7 mm wheals is considered the endpoint. The advantage of a serial dilution method over prick testing is that all levels of allergy, including the more subtle, will be identified. Additionally, the presence of a second test confirmation wheal virtually excludes aberrant skin responses. Finally, not only are the allergens identified, but the level of their sensitivity is known, allowing immunotherapy vials to be prepared with a concentration of antigen specific to the patient’s identified needs. This would suggest a safe course of immunotherapy, as well as a therapy tailored to begin at the exact level of sensitivity of each individual antigen.14–16 Despite these apparent advantages to the intradermal dilution method, no superiority of this method in terms or safety or efficacy has been identified.
Fornadley
FIGURE 2. Blending of prick and intradermal testing. MQT = modified quantitative testing.
Blending testing type, prick, and intradermal: modified quantitative testing There had been a need for allergy testing that has more quantification than simple prick testing, yet did not require the time and resources of skin endpoint titration. It was also desirable for clinicians to have information on relative sensitivities in order to make up a safe, effective starting vial for immunotherapy. Krouse and Krouse17 reported a method which blended skin-prick testing with intradermal testing that provides the relative antigen sensitivity information. This has been termed modified quantitative testing (MQT).17 This technique is based on the observation that multi-prick testing elicits a skin response approximately equivalent to between a #3 and #4 dilution of the serial dilution testing method, but at a safe superficial level of the skin. Once the result of the prick test is known, the algorithm is entered (Fig. 2). In some cases, the prick test alone is sufficient to determine the presence and level of antigen sensitivity. In other arms of the algorithm, 1 intradermal test is required to confirm allergy and determine the correct dilution for initiating immunotherapy.13 This allows the safe determination of allergy sensitivity without the entire intradermal titration series, but still permits allergy immunotherapy to be safely initiated at a level of concentration unique to each tested antigen. Immunotherapy based upon MQT has been shown to modulate immune mediators in a manner consistent with successful immunotherapy techniques.17 This “blending” of skin-prick testing with single intradermal tests closely approximates other prick test–based techniques, but with the advantage of having semiquantitative data on each antigen’s sensitivity level to determine the starting strength for immunotherapy. This benefit of quantitative testing has been considered by King and other authors5, 14, 15 as vital to safe immunotherapy.
Precautions Although skin testing is generally accepted as a safe modality, there are very low risks of developing adverse reactions to skin testing, including reports of anaphylaxis and death with both prick and intradermal testing.18 Therefore, practitioners who perform skin testing must be able to promptly recognized and treat potential adverse reactions to skin testing. In addition, there are limitations to the utility of skin testing. Skin testing cannot provide a satisfactory interpretation in a patient with hyperresponsive skin (dermatographism), or skin with substantial dermatitis and/or infection. Negative and positive controls must be used. Patients must not be taking medications that will limit or conceal the allergenic response, such as antihistamines or certain chemotherapeutic agents. Finally, beta-blocker therapy will not change the patient’s response, but if a serious systemic reaction occurs, beta-blockers can interact adversely with the epinephrine that would otherwise be used to treat the reaction.18
Conclusion Skin-prick testing and intradermal testing are the primary categories of skin testing; many forms of accepted skin testing are available, and there are reasonable justifications for practitioners selecting different types of testing. Caution must be taken to avoid creating a serious systemic reaction by injecting an injudicious amount of antigen into the skin, or in skin-testing a patient whose medical condition or medication profile puts them at increased risk.
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
S44
Skin testing for inhalant allergy
References 1.
2.
3.
4.
5.
6.
S45
Leonardi A, Motterle L, Bortolotti M. Allergy and the eye. Clin Exp Immunol. 2008;153(Suppl 1): 17–21. Anantasit N, Vilaiyuk S, Kamchaisatian W, et al. Comparison of conjunctival and nasal provocation tests in allergic rhinitis children with Dermatophagoides pteronyssinus sensitization. Asian Pac J Allergy Immunol. 2013;31:227–232. Ellis AK, North ML, Walker T, Steacy LM. Environmental exposure unit: a sensitive, specific, and reproducible methodology for allergen challenge. Ann Allergy Asthma Immunol. 2013;111:323–328. Heinzerling L, Mari A, Bergmann KC, et al. The skin prick test - European standards. Clin Transl Allergy. 2013;3:3. Boyd EL. Cutaneous testing for allergy diagnosis: comparison of methods in common use. Otolaryngol Clin North Am. 2003;36:869–877. [No authors listed]. American Medical Association Council on Scientific Affairs. In vivo diagnostic testing and immunotherapy for allergy. Report I, Part I, of the allergy panel. Council on Scientific Affairs. JAMA. 1987;258:1363–1367.
7.
Masse MS, Granger Vall´ee A, Chiriac A, et al. Comparison of five techniques of skin prick tests used routinely in Europe. Allergy. 2011;66:1415–1419. 8. Demoly F, et al. In vivo methods for study of allergy skin tests, techniques and interpretation. In: Middleton E, Adkinson NF, Busse WW, Ellis EF, Reed CE. Allergy Principles and Practice. Vol 1. 5th ed. St. Louis: Mosby; 1998:430–439. 9. Huber B, Berdel D. A comparison of the multi-test with the prick test and multi-test 2. Clin Allergy. 1983;13:467–472. 10. Dykewicz MS, Dooms KT, Chassaing DL. Comparison of the Multi-Test II and ComforTen allergy skin test devices. Allergy Asthma Proc. 2011;32:198–202. 11. Wood RA, Phipatanakul W, Hamilton RG, Eggleston PA. A comparison of skin prick tests, intradermal skin tests, and RASTs in the diagnosis of cat allergy. J Allergy Clin Immunol. 1999;103(5 Pt 1):773–779. 12. Nelson HS, Oppenheimer J, Buchmeier A, Kordash TR, Freshwater LL. An assessment of the role of intradermal skin testing in the diagnosis of clinically relevant allergy to timothy grass. J Allergy Clin Immunol. 1996;97:1193–1201.
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
13. McKay SP, Meslemani D, Stachler RJ, Krouse JH. Intradermal positivity after negative prick testing for inhalants. Otolaryngol Head Neck Surg. 2006;135:232–235. 14. King HC. Skin endpoint titration. Still the standard? Otolaryngol Clin North Am. 1992;25:13–25. 15. King HC, Mabry RL, Mabry CS, Gordon BR, Marple BF. Interaction with the patient. In: Allergy in ENT Practice: The Basic Guide. 2nd ed. New York: Thieme Medical Publishers; 2005:67–104. 16. Gordon BR, Hurst DS, Fornadley JA, Hunsaker DH. Safety of intradermal skin tests for inhalants and foods: a prospective study. Int Forum Allergy Rhinol. 2013;3:171–176. 17. Krouse JH, Krouse HJ. Modulation of immune mediators with MQT-based immunotherapy. Otolaryngol Head Neck Surg. 2006;134:746–750. 18. Bernstein IL, Li JT, Bernstein DI, et al.; American Academy of Allergy, Asthma and Immunology; American College of Allergy, Asthma and Immunology. Allergy diagnostic testing: an updated practice parameter. Ann Allergy Asthma Immunol. 2008;100(Suppl 3):S1–S148.
Skin testing for inhalant allergy John A. Fornadley, MD, FAAOA
Background: Allergy is diagnosed by a combination of history, physical examination, and confirmatory testing. Modalities for testing include skin testing, in vitro assessment, and challenge testing of the conjunctiva or nasal mucosa. Challenge testing is primarily reserved for research. Methods: A review of the literature on skin testing methods for inhalant allergic rhinitis was performed. Results: Different forms of commonly used skin testing are available, including: individual prick; multiple prick; single, intradermal, and intradermal dilutional testing; and blended techniques. Each has inherent benefits and limitations. Conclusion: Skin testing remains a valid and in some cases superior means of identifying inhalant allergy. Skin-prick
S
pecific allergen testing in patients with a history and physical exam suspicious for inhalant allergy is indicated when knowledge of the patient’s sensitivities would lead to improvement in patient care. This testing can be performed by skin or laboratory (in vitro, specific immunoglobulin E [sIgE] blood testing) assessment. Typically, patients are tested with pertinent allergens based on history and geographic location because seasonal allergens in particular can vary by region. The results of such testing can provide important information, starting by identifying the presence or absence of allergy. This permits assessment of allergy as distiguished from other, nonallergic conditions, including nonallergic rhinitis with eosinophilia (NARES), irritant rhinitis, or vasomotor rhinitis, which can mimic or augment allergic disease. In addition, identification of specific allergens to which the patient is sensitive can allow therapy to be directed appropriately. Knowing the sen-
Clinical Associate Professor of Surgery, Division of Otolaryngology Penn State University, Hershey, PA Correspondence to: John A. Fornadley, MD, FAAOA, Penn State University, 1650 Brookline Drive, Hummelstown, PA 17036; e-mail: [email protected] Potential conflict of interest: J.A.F. is a stockholder, Glaxo SmithKline, Johnson and Johnson. Received: 30 June 2014; Revised: 3 July 2014; Accepted: 3 July 2014 DOI: 10.1002/alr.21393 View this article online at wileyonlinelibrary.com.
S41
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
testing and intradermal testing are the primary categories, although different formats exist for each. Caution must be taken to avoid creating a serious systemic reaction by injecting an injudicious amount of antigen into the skin, or in skin testing a patient whose medication profile puts them C 2014 ARS-AAOA, LLC. at increased risk.
Key Words: allergy testing; allergy test techniques; intradermal testing; modified quantitative testing; prick-puncture testing; skin testing How to Cite this Article: Fornadley JA. Skin testing for inhalant allergy. Int Forum Allergy Rhinol. 2014;4:S41–S45.
sitivities may guide environmental interventions, such as removing an animal from the environment, or selecting appropriate medications during the season when the specific allergen is present. Immunotherapy also requires knowledge of the specific allergen. Until the characterization of IgE in the 1960s and subsequent development of sIgE assays for this molecule, specific allergen testing could only be performed by direct challenge to the body. The primary organ for this testing has been the skin, although nasal, conjunctival, and bronchial routes of challenge have been described.1–3 The skin allows for a reasonably safe, reproducible, and visible region for evaluation of allergic response. Skin testing results can be semiquantitatively evaluated with less patient morbidity than would occur with testing the conjunctiva, nasal mucosa, or tracheobronchial tree. As the primary testing modality for the first 50 years of allergy therapy, skin testing has been studied extensively and refined. Even with development of in vitro assays for sIgE, skin testing remains an important, in many cases primary, means of testing individuals for allergy. There are several advantages of skin testing.4 The results are more rapid, with the skin reactivity read within 15 to 20 minutes, whereas with sIgE testing blood must be drawn in a laboratory and results typically take 1 to 2 days. Often, skin testing is a less costly modality than sIgE testing. The ability of the patient to experience firsthand the reaction
Fornadley
caused by the test antigens can be helpful in gaining the patient’s appreciation of the extent and severity of the disease process. Despite the prolonged experience with this modality, skin testing is subject to variability due to the technique, the risk of abnormally increased skin sensitivity, and the individual performing the test. There is also a subjective component to result interpretation.5 Skin testing techniques for inhalant allergens can be divided into epicutaneous (prick, prick-puncture) and intracutaneous (intradermal) techniques influence on outcomes. There are variations on each technique, and both modalities have a role in the correct identification of IgE-mediated allergy.
Epicutaneous testing
[IV]) needle against several commonly used lancet-type and solid (non-hypodermic) needles. The IV needle and metal lancets were judged to be the most satisfactory for reproducible testing results in comparison with other prick testing systems.7 In a nonsensitized patient, the epicutaneous prick test will not cause a local skin reaction. However, if an IgE-mediated sensitization exists, there will be release of histamine and development of a wheal (raised skin swelling reaction) from increased vascular permeability. Additionally, inflammatory mediators will create vasodilation, which results in a flare response (redness). Both the wheal and flare have been used to diagnose allergy.
Multiple-allergen prick-testing systems
Despite the advantages that have been identified for skin testing, the protective barrier function of the skin meant that it could not be tested in the same way as the antigen was applied directly to nasal mucosa, conjunctiva, or tracheobronchial tree. The presence of hair, oils, and keratinized epithelium limited the ability to identify all but the most dramatic sensitivities. Initial skin testing required placement of a small abrasion (“scratch testing”) to allow antigen access to a more sensitive, but still quite superficial, layer of skin. This method allowed successful identification of response to an allergen, but the variability in skin thickness, and technical difficulties creating a uniform scratch size and depth drastically limited the success of this technique. Therefore, scratch testing is no longer a recommended allergy testing modality.6 Derived from scratch testing, epicutaneous tests, also termed prick or prick-puncture, allow testing in the upper levels of skin. Concentrated antigen is delivered into the epicutaneous levels of skin by the use of a needle. This can be an intravenous (IV) type or a solid (non-hypodermic) needle. Skin-prick testing is generally more comfortable and safer than intradermal techniques that place antigen deeper into the skin. Because prick testing places allergen in a more superficial layer of skin, there is a decreased risk of provoking a systemic response in comparison to intradermal testing, in which the allergen in delivered deeper into the skin.
Individual prick testing causes minimal discomfort and is relatively inexpensive but can be time consuming and userdependent.8 In response to individual prick testing’s limitations, multiple simultaneous prick testing systems were developed that allow for placement of several allergens for testing with 1 application.9 The use of multiple-allergen skin-prick systems allows several antigens to be placed on the skin at 1 time. In addition to saving time, these devices more equally distribute the pressure exerted by each needle. Multiple test systems have multiple tines on each head; these tines can be dipped into a tray of wells containing different allergen extracts. The tines carry the allergen by capillary action. The benefit to these multiple-allergy prick tests includes more rapid testing and less technique-dependent influence on outcomes. There are different types of multiple-prick testing systems that vary in sensitivity and specificity. Dykewicz et al.10 reviewed 2 common multiple-prick testing devices, the Multi-test II (Lincoln Diagnostics, Decatur, IL) and the ComforTen (Allergy Laboratories, Oklahoma City, OK). The authors reported that the Multi-test II had lower coefficients of variability, greater wheal size, and higher sensitivity, but similar specificity to the ComfotTen. Overall, one should recognize that not all prick testing systems are the same and the results should be interpreted based upon the system used, because each system has specific instructions for interpretation included in the products based upon the wheal and flare responses elicited.
Individual prick testing
Intradermal testing
The back or volar surfaces of the arms provide ample skin surface for allergy testing and are of a relatively uniform thickness with less tendency to be hair-bearing. One drop of antigen concentrate for each individual antigen is placed on the skin. A single needle or lancet is passed through the antigen droplet and pricks the skin. The antigen is carried into the superficial skin area by the device at a reproducible quantity and depth. The current recommendation is to use 1 needle for each antigen.4 A variety of needles have been used for skin-prick testing. A recent review compared a hollow (hypodermic type
Although prick testing has been found to be quite specific, there may be concerns regarding a lower sensitivity (false negative). Injection of an antigen into the deeper layers of the skin can permit identification of a clinically significant allergen that was either not detected or is equivocally positive by skin-prick testing. Placement of an intradermal wheal places more antigen into deeper tissues that are beneath the epidermis, assuring that antigen comes in contact with vital (nonkeratinized) tissue. The disadvantage of intradermal testing is the risk of adverse reaction. Injecting concentrated antigen into more
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
S42
Skin testing for inhalant allergy
vascularized levels of the skin would risk a reaction that is unacceptably severe, including anaphylaxis.5 There are 2 methods available to clinicians to overcome this problem and harvest the useful information available from intradermal testing. The first method allowing safe injection of intradermal antigen is to perform the skin-prick testing first. If a positive response is observed, it will be clear that the patient is sensitive to the antigen, and no intradermal testing will be needed. On the contrary, the absence of a response on prick testing would alert the tester that an intradermal test wheal could be safely tolerated by the patient. This circumstance is most likely to arise when a patient’s history is markedly positive for an antigen, yet the prick testing does not confirm allergy. The intradermal test in this may identify allergic sensitization when skin-prick testing is negative. The clinical interpretation of a positive intradermal test after a negative skin-prick test is controversial. Some studies have demonstrated that a positive intradermal test after a negative skin-prick test does not correlate with allergy symptoms using either a pollen season11 or exposure to cats.12 Clinical interpretation is required based on knowledge of both the allergen and the patient. The second method that allows the safe use of intradermal injections is a serial dilution technique. In this technique, the concentrated antigen is diluted thousandsfold, until the antigen preparation is sufficiently dilute to pose minimal or no threat of anaphylaxis.13–15 Dilutions have been described using a 1:3, 1:5, or 1:10 calculations. King14 and King et al.15 summarized allergy testing using 1:5 dilutions of a commercial concentrate in the classic intradermal dilutional testing (IDT) method. Taking concentrated 1:20 wt/vol antigen and diluting this with saline, progressive dilutions of 1:100 (dilution #1), 1:500 (dilution #2), 1:2500 (dilution #3), etc. are created. A small quantity, approximately 0.04 mL, of the sixth 1:5 dilution (termed a #6 dilution) is injected intradermally to create a 4-mm wheal in the skin. This is observed for 10 to 15 minutes. In the nonallergic patient, due to skin laxity, the wheal grows slightly, to perhaps 5 mm, even in the absence of an allergic response. If there is minimal growth of this wheal, it is safe to move to a dilution of concentrate that is 5-fold more concentrated (the #5 dilution), and repeat the process. If the patient is allergic, the wheal will grow by at least 2 to 3 mm (approximately a 7-mm to 8-mm wheal). The choice of 5-fold dilution assures that the increase in antigen concentration is small enough that skin reaction should not exceed 2 to 3 mm. In the allergic patient, this series of skin reactions of progressively more concentrated intradermal tests, the skin reactions will show a wheal that grows by at least 2 mm to 7 mm or more (the “endpoint” wheal), and an additional wheal that also grows by at least 2 mm to 9 mm or more (the “confirming” wheal). The information identifies the patient as allergic, and the endpoint identifies the concentration of antigen at which immunotherapy can be safely initiated (Fig. 1). In the
S43
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
FIGURE 1. Intradermal dilutional testing positive whealing response.
case of a negative test to an allergen, as each more concentrated antigen solution is placed without a noted response, the test reaches a point where a sufficiently strong concentration of the antigen has been injected without reaction to assure that the individual is truly not allergic to the allergen being tested. Usually this would be the first or second dilution of the concentrate. The method of IDT (formerly called skin endpoint titration) has historically been considered as a “standalone” form of allergy testing that does not use skin-prick testing at all. Two aberrant skin responses to IDT have been described that one should be aware of: (1) the flash response, and (2) the plateau response.15 The flash response is one where there is an abnormally large wheal that develops with IDT after several negative wheals; when this occurs it is recommended to stop testing so that a systemic reaction is not provoked and to retest that allergen on another day. This flash response is thought to be due to cross-reactivity to foods ingested and/or environmental allergens in season at the time of testing. The plateau response occurs when there is a positive wheal (7 mm) that is followed by several wheals of the same size (several more 7-mm wheals) before a confirming wheal (9 mm) occurs. In this circumstance the first of the 7 mm wheals is considered the endpoint. The advantage of a serial dilution method over prick testing is that all levels of allergy, including the more subtle, will be identified. Additionally, the presence of a second test confirmation wheal virtually excludes aberrant skin responses. Finally, not only are the allergens identified, but the level of their sensitivity is known, allowing immunotherapy vials to be prepared with a concentration of antigen specific to the patient’s identified needs. This would suggest a safe course of immunotherapy, as well as a therapy tailored to begin at the exact level of sensitivity of each individual antigen.14–16 Despite these apparent advantages to the intradermal dilution method, no superiority of this method in terms or safety or efficacy has been identified.
Fornadley
FIGURE 2. Blending of prick and intradermal testing. MQT = modified quantitative testing.
Blending testing type, prick, and intradermal: modified quantitative testing There had been a need for allergy testing that has more quantification than simple prick testing, yet did not require the time and resources of skin endpoint titration. It was also desirable for clinicians to have information on relative sensitivities in order to make up a safe, effective starting vial for immunotherapy. Krouse and Krouse17 reported a method which blended skin-prick testing with intradermal testing that provides the relative antigen sensitivity information. This has been termed modified quantitative testing (MQT).17 This technique is based on the observation that multi-prick testing elicits a skin response approximately equivalent to between a #3 and #4 dilution of the serial dilution testing method, but at a safe superficial level of the skin. Once the result of the prick test is known, the algorithm is entered (Fig. 2). In some cases, the prick test alone is sufficient to determine the presence and level of antigen sensitivity. In other arms of the algorithm, 1 intradermal test is required to confirm allergy and determine the correct dilution for initiating immunotherapy.13 This allows the safe determination of allergy sensitivity without the entire intradermal titration series, but still permits allergy immunotherapy to be safely initiated at a level of concentration unique to each tested antigen. Immunotherapy based upon MQT has been shown to modulate immune mediators in a manner consistent with successful immunotherapy techniques.17 This “blending” of skin-prick testing with single intradermal tests closely approximates other prick test–based techniques, but with the advantage of having semiquantitative data on each antigen’s sensitivity level to determine the starting strength for immunotherapy. This benefit of quantitative testing has been considered by King and other authors5, 14, 15 as vital to safe immunotherapy.
Precautions Although skin testing is generally accepted as a safe modality, there are very low risks of developing adverse reactions to skin testing, including reports of anaphylaxis and death with both prick and intradermal testing.18 Therefore, practitioners who perform skin testing must be able to promptly recognized and treat potential adverse reactions to skin testing. In addition, there are limitations to the utility of skin testing. Skin testing cannot provide a satisfactory interpretation in a patient with hyperresponsive skin (dermatographism), or skin with substantial dermatitis and/or infection. Negative and positive controls must be used. Patients must not be taking medications that will limit or conceal the allergenic response, such as antihistamines or certain chemotherapeutic agents. Finally, beta-blocker therapy will not change the patient’s response, but if a serious systemic reaction occurs, beta-blockers can interact adversely with the epinephrine that would otherwise be used to treat the reaction.18
Conclusion Skin-prick testing and intradermal testing are the primary categories of skin testing; many forms of accepted skin testing are available, and there are reasonable justifications for practitioners selecting different types of testing. Caution must be taken to avoid creating a serious systemic reaction by injecting an injudicious amount of antigen into the skin, or in skin-testing a patient whose medical condition or medication profile puts them at increased risk.
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
S44
Skin testing for inhalant allergy
References 1.
2.
3.
4.
5.
6.
S45
Leonardi A, Motterle L, Bortolotti M. Allergy and the eye. Clin Exp Immunol. 2008;153(Suppl 1): 17–21. Anantasit N, Vilaiyuk S, Kamchaisatian W, et al. Comparison of conjunctival and nasal provocation tests in allergic rhinitis children with Dermatophagoides pteronyssinus sensitization. Asian Pac J Allergy Immunol. 2013;31:227–232. Ellis AK, North ML, Walker T, Steacy LM. Environmental exposure unit: a sensitive, specific, and reproducible methodology for allergen challenge. Ann Allergy Asthma Immunol. 2013;111:323–328. Heinzerling L, Mari A, Bergmann KC, et al. The skin prick test - European standards. Clin Transl Allergy. 2013;3:3. Boyd EL. Cutaneous testing for allergy diagnosis: comparison of methods in common use. Otolaryngol Clin North Am. 2003;36:869–877. [No authors listed]. American Medical Association Council on Scientific Affairs. In vivo diagnostic testing and immunotherapy for allergy. Report I, Part I, of the allergy panel. Council on Scientific Affairs. JAMA. 1987;258:1363–1367.
7.
Masse MS, Granger Vall´ee A, Chiriac A, et al. Comparison of five techniques of skin prick tests used routinely in Europe. Allergy. 2011;66:1415–1419. 8. Demoly F, et al. In vivo methods for study of allergy skin tests, techniques and interpretation. In: Middleton E, Adkinson NF, Busse WW, Ellis EF, Reed CE. Allergy Principles and Practice. Vol 1. 5th ed. St. Louis: Mosby; 1998:430–439. 9. Huber B, Berdel D. A comparison of the multi-test with the prick test and multi-test 2. Clin Allergy. 1983;13:467–472. 10. Dykewicz MS, Dooms KT, Chassaing DL. Comparison of the Multi-Test II and ComforTen allergy skin test devices. Allergy Asthma Proc. 2011;32:198–202. 11. Wood RA, Phipatanakul W, Hamilton RG, Eggleston PA. A comparison of skin prick tests, intradermal skin tests, and RASTs in the diagnosis of cat allergy. J Allergy Clin Immunol. 1999;103(5 Pt 1):773–779. 12. Nelson HS, Oppenheimer J, Buchmeier A, Kordash TR, Freshwater LL. An assessment of the role of intradermal skin testing in the diagnosis of clinically relevant allergy to timothy grass. J Allergy Clin Immunol. 1996;97:1193–1201.
International Forum of Allergy & Rhinology, Vol. 4, No. S2, September 2014
13. McKay SP, Meslemani D, Stachler RJ, Krouse JH. Intradermal positivity after negative prick testing for inhalants. Otolaryngol Head Neck Surg. 2006;135:232–235. 14. King HC. Skin endpoint titration. Still the standard? Otolaryngol Clin North Am. 1992;25:13–25. 15. King HC, Mabry RL, Mabry CS, Gordon BR, Marple BF. Interaction with the patient. In: Allergy in ENT Practice: The Basic Guide. 2nd ed. New York: Thieme Medical Publishers; 2005:67–104. 16. Gordon BR, Hurst DS, Fornadley JA, Hunsaker DH. Safety of intradermal skin tests for inhalants and foods: a prospective study. Int Forum Allergy Rhinol. 2013;3:171–176. 17. Krouse JH, Krouse HJ. Modulation of immune mediators with MQT-based immunotherapy. Otolaryngol Head Neck Surg. 2006;134:746–750. 18. Bernstein IL, Li JT, Bernstein DI, et al.; American Academy of Allergy, Asthma and Immunology; American College of Allergy, Asthma and Immunology. Allergy diagnostic testing: an updated practice parameter. Ann Allergy Asthma Immunol. 2008;100(Suppl 3):S1–S148.
