Dictionary of Allergies .. Basophil activation test

The basophil activation test determines the percentage of basophils which express CD63 as an activation marker, by means of flow cytometry, after in vitro stimulation with allergen, using double labelling with monoclonal antibody anti-CD63-PE and anti-IgE-FITC [1]. The basophil activation test is a highly reliable technique in the diagnosis of allergy to inhalant allergens. The sensitivity of the basophil activation test was 93.3%, and its specificity 98.4%, when using a cut-off point of 15% activated basophils as positive result. The basophil activation test is a particularly useful technique in the diagnosis of patients with IgE mediated allergy to betalactams and allows the identification of 50% of patients. Used in conjunction with CAP, it allows the identification of 65.5% of such patients [2]. Diagnosis of stinging insect allergy is based on a detailed history, venom skin tests, and detection of venom-specific IgE.

As an additional diagnostic tool, basophil responsiveness to venom allergens has been shown to be helpful in selected patients. The BAT may be used as an additional test to confirm the diagnosis of stinging insect allergy in selected patients, provided that it is performed by an experienced laboratory using a validated assay. Test results have to be interpreted by clinicians familiar with the methodological aspects.

The utility of the BAT to confirm allergy diagnosis and to predict the risk of subsequent systemic reactions may be improved by combined analysis of multiple surface markers and intracellular signaling pathways[3]. Diagnosis of drug allergy is not always straight forward for several reasons. First, a broad spectrum of drugs can elicit various immune-mediated diseases with distinct pathomechanism, secondly, although exact epitope identification is not mandatory for clinical diagnosis, the epitope that causes the reaction is frequently unknown, thirdly in vitro or in vivo test results might not be predictive of a clinical situation, and finally the gold standard or reference test for diagnosis, the drug challenge, is a complicated and sometimes dangerous endeavour. Upon challenge with specific allergens that cross-link membrane-bound IgE antibodies, basophils upregulate the expression of different activation markers such as CD63 and CD203c.

These immunophenotypic alterations can be detected on a single-cell basis by multicolour flow cytometry using specific monoclonal antibodies in the basophil activation test (BAT) [6]. At present, basophil activation using CD63 and CD203c does not seem to be optimally sensitive for the diagnosis of ASA sensitivity[4]. Sanz ML,  et al (2009) demonstrated that  BAT sensitivity in beta-lactam allergy was 50%, and specificity ranged from 89 to 97%. There are several studies to validate the BAT in allergy to muscle relaxants showing a sensitivity ranging from 54 to 64% with a specificity of 100 and 93%.

The sensitivity of a test for evaluating immediate allergic reactions to drugs may decrease over time. To date, the BAT is the only in-vitro diagnostic method that has been validated for the diagnosis of both IgE-mediated and hypersensitivity reactions to NSAIDs. With respect to other drugs, they are nonetheless interesting as they include the evaluation of allergy to drugs that cannot be studied by other in-vitro techniques. All these data suggest that although a full validation of the test is required, BAT is a potential diagnostic method for evaluating immediate allergic reactions to drugs and NSAID hypersensitivity reactions [5]. Basophil activation test should be performed as early as possible after taking the blood sample, preferably within 4 h. In contrast to the skin test, BAT can be performed in patients undergoing treatment with antihistamines. For reasons of multiple influencing factors, BAT should be performed only at validated laboratories[7].

References

1. Sanz, M. L., et al: Allergen-induced basophil activation: CD63 cell expression detected by flow cytometry in patients allergic to Dermatophagoides pteronyssinus and Lolium perenne. Clinical & Experimental Allergy, 2001:31(7):1007.

2. Sanz, M. L.et al: Flow cytometric basophil activation test by detection of CD63 expression in patients with immediate type reactions to betalactam antibiotics. Clinical & Experimental Allergy 2002: 32(2): 277.

3. Scherer K, Bircher AJ, Heijnen IA. Diagnosis of stinging insect allergy: utility of cellular in-vitro tests. Curr Opin Allergy Clin Immunol.2009 Jun 16.

4. Bavbek S, Ikincioğulları A, Dursun AB, Güloğlu D, Arıkan M, Elhan AH, Mısırlıgil Z. Upregulation of CD63 or CD203c Alone or in Combination Is Not Sensitive in the Diagnosis of Nonsteroidal Anti-Inflammatory Drug Intolerance. Int Arch Allergy Immunol.2009 Jun 4;150(3):261-270.

5. Sanz ML, Gamboa PM, Mayorga C. Basophil activation tests in the evaluation of immediate drug hypersensitivity. Curr Opin Allergy Clin Immunol.2009 May 28.

6. Ebo DG, Hagendorens MM, Bridts CH, De Clerck LS, Stevens WJ. The basophil activation test in immediate drug allergy. Acta Clin Belg. 2009 Mar-Apr;64(2):129-35.

7. , Aberer W. The basophil activation test in the diagnosis of allergy: technical issues and critical factors. Allergy. 2009 Feb 20.