Comparison of two in vitro assays, RAST and CAP, when applied to the diagnosis of anaphylactic reactions to honeybee or yellow jacket venoms. Correlation with history and skin tests.

We compared the results obtained with a new specific IgE assay (Pharmacia CAP system) to those of RAST and intradermal skin tests (ST) performed in 87 patients with a history of generalized reaction to honeybee or yellow jacket venom. When CAP and RAST were compared with positive ST performed with honeybee venom, CAP sensitivity was not significantly higher (98%) than that of RAST (95%). When yellow jacket venom was tested, CAP sensitivity (93%) was clearly superior to that of RAST (40%). When we compared the specificities of RAST and CAP to bee venom, RAST was positive in 21% of the 24 subjects with negative ST, and CAP in 42%. Among the 29 patients with negative ST to yellow jacket venom, RAST was positive in 17% and CAP in 28%. These results do not reflect a lower specificity of CAP, because CAP positivities could be inhibited in vitro, and because, in three patients with a history of anaphylactic reaction (one to honeybee, two to yellow jacket), CAP was the only positive test confirming the clinical observation. Among the 53 patients who were able to identify the offending insect (honeybee, 31; yellow jacket, 22), the cause of the anaphylactic reaction was usually confirmed by ST and CAP: honeybee venom 97% for both ST and CAP; yellow jacket venom 82% for ST, 86% for CAP. This was not the case for RAST, which confirmed honeybee venom hypersensitivity in 87% and yellow jacket venom hypersensitivity in only 41%. Thus, CAP is both more sensitive and more rapid than RAST, without losing specificity.