POSITIVE ALLERGOLOGICAL TESTS MAY TURN NEGATIVE WITH NO FURTHER EXPOSURE TO THE SPECIFIC ALLERGEN - A LONG-TERM, PROSPECTIVE, FOLLOW-UP-STUDY IN PATIENTS ALLERGIC TO PENICILLIN

Preliminary literature reports suggest the possibility that, in an all ergic patient, a previously positive allergological test may turn nega tive after a long period of time with no further exposure to the speci fic allergen. The aim of this study was to evaluate the rate by which a previously positive skin test or RAST may turn negative in a group o f patients allergic to penicillin if no further exposure to the specif ic allergen occurs. Sixty-three patients allergic to penicillin (48 wi th type I allergy and 15 with type IV allergy) were enrolled in a long -term, prospective, follow-up study, undergoing a successive complete allergological testing within 6 years of the first positive examinatio n. During the follow-up period, skin tests progressively became negati ve in 28 (58.3%) type I allergic patients and in only one (6.7%) subje ct with type IV allergy. Similarly, the positive RAST turned negative in as many as 13 subjects (43.3% of cases). The cumulative skin test p ositivity (type I allergy) was significantly lower than that of patch tests (type IV allergy) (chi(2) = 10.4; d.f. = 1; p < 0.005, Logrank t est). No significant difference in the progressive rate of decrease in skin test and RAST cumulative positivity was observed in the 30 patie nts showing both RAST and skin test positivity on entering the follow- up study. Our results provide strong evidence that a positive allergol ogical test performed in a drug-allergic patient may become negative w ith time, in the absence of further exposure to the specific antigen. A negative allergological test cannot, therefore, rule out the immunol ogical basis of a drug sensitivity. This is why we always suggest advi sing patients with a personal history of drug hypersensitivity against any further administration of the responsible drug, even in the prese nce of a completely negative allergological examination.