The Basophil Activation Test (BAT)
The BAT is a useful diagnostic tool for immediate IgE-mediated reactions to both foods and drugs. Its major limitation is the low count of basophil in peripheral blood, but recent flow cytometric techniques have allowed the use of whole blood samples and more accurate determination of the levels of different markers. Its other pitfall is the low sensitivity and this problem is tackled by using different cut off values when evaluating activation markers by flow cytometry. However, the timing of the test with regard to the initial reaction is very critical as the test tends to lose its sensitivity with time. On the other hand, time during which basophils maintain their activity after blood sampling seems to be short and it has been recommended that samples are processed within 3 h of sampling, which limits the availability of the test. The test is quite reproducible but only when used with a limited number of standardized drugs.
Basophils are effector cells in immediate-type hypersensitivity reactions and they respond to antigen stimulation in vitro by degranulation (e.g. release of histamine and leukotrienes) and expression of certain surface markers including CD45, CD11b, CD11c, CD62L, CD203c and CD63. Originally, the BAT was performed by measuring the release of histamine. Alternatively, flow cytometry based techniques are now used to measure specific surface markers that are up-regulated during basophil activation. The most commonly used are the antigens CD63, also known as lysosomal-associated membrane glycoprotein-3 (LAMP-3) and CD203c, a glycosylated type II transmembrane molecule.
The BAT has been validated for type I reactions to muscle relaxants, β-lactam antibiotics, pyrazolones and NSAIDs. Sensitivity of the test for reactions to β-lactam antibiotics, quinolones and rocuonium was reported as 33–67%, 71.1% and 80%, respectively.
