Basophil Activation Tests
A very different approach postulates that the level of basophil sensitivity is of clinical significance because it modulates the specific IgE in relation to the allergic reaction to a sting. There is a long history in the literature of allusion to such 'twitchy mast cells', 'basophil hyper-releasability', and 'leaky basophils'. This heightened level of activation, which may stop short of actual mediator release, could be the result of many intracellular signaling processes, and can be monitored by the expression on the cell surface of basophil activation markers such as CD63 and CD203c.
One of the problems in translation of basophil activation tests (BATs) from a research tool to a routine clinical test is the need for a uniform and standard approach to the methodology, and the reporting and analysis of the results. Kosnik et al. initially reported a ratio of 'positive' activation to 1.0 vs. 0.1 μg/ml of venom. This 'positive activation' is the proportion of basophils showing increased CD63 expression in response to allergen using a cutoff that varies in different studies, usually in the range of 10–15%. More recently, the 'CD-sens' is used to represent the inverse of the concentration for maximal CD63 response. Other studies continue to report the absolute response to a single-concentration venom, and some studies still find the CD203c expression to correlate with some clinical outcomes.
Nevertheless, a growing literature attests to the potential utility of the test. The BAT was more sensitive than intradermal skin tests in patients suffering from clinical allergy with negative serum IgE and skin prick tests, especially in patients with mastocytosis. Although recombinant venom allergens have shown some utility in detecting clinical insect allergy in patients with negative tests for serum IgE to native venoms, the BAT was reported to be superior in such cases. The BAT was highly correlated with the frequency of systemic reactions to VIT and with successful protection during VIT, and predicted the relapse of patients after stopping VIT. Eberlein et al. has described a refinement of the BAT using recombinant venom allergens for improved diagnostic accuracy.