The frequency and clinical significance of specific IgE to both wasp (Vespula) and honey-bee (Apis) venoms in the same patient.

BACKGROUND

Changeover from Phadebas RAST to Pharmacia AutoCAP increased double-positivity to both honey-bee and common wasp (vespula) venom in our patients.

OBJECTIVE

We examined the frequency of IgE double-positivity, its clinical relevance and utility in investigating potentially allergic patients.

METHODS

One hundred and eighty-two patients with hymenoptera allergy were tested using RAST (n = 51) and AutoCAP (n = 131) assays over 4 years. Patients had a history of reactions to vespulae (22), honey-bee (10) and unidentified hymenoptera (vespinae) (7).

RESULTS

After changing from RAST to AutoCAP double-positivity increased from 10 (5/ 51) to 30% (39/131) (P < 0.01). RAST and CAP assays gave similar median class results (vespula = 3, honey-bee = 2). Thirty-six CAP patients had systemic reactions of Mueller grade II and above. In vespula-allergic double-positive subjects, high CAP classes (> or = class 3) to honey-bee were common (30%). In 25% the CAP classes were equal. In honey-bee-allergic subjects, all vespula venom CAP IgE was low titre (class 1 or 2) and 20% were equal for both venoms. In 43% of vespinae-allergic patients the CAP class was equal to both (class 2 and 3). In contrast, intradermal skin test double-positivity was uncommon. Double-negative skin test results were common in the CAP double-positive population (22% of honey-bee-allergic, 13% of vespula-allergic and 43% of vespinae-allergic patients). Vespula allergic patients have higher bee-venom IgE than vice versa. Twenty-seven per cent of CAP double-positive patients (representing 8% of all venom allergic patients tested over this period) had equal class IgE to both venoms which was not helpful in diagnosis. Combination of skin testing and CAP is unhelpful in only 5/37 (14%) of patients with double-positive serology.

CONCLUSION

If used in isolation CAP may be misleading, especially if only one venom is tested. Identification of the causative venom must utilize both clinical history and skin testing in these double-positive patients, and challenge testing if indicated.