The usefulness of skin tests to prove drug hypersensitivity.

BACKGROUND: Suspected drug hypersensitivity is common. Only a minority of cutaneous adverse drug reactions (CADRs) are allergic in origin and will reappear after the next exposure. Methods to confirm suspected CADRs are needed and skin testing could serve as one possibility.

OBJECTIVES: To analyse the usefulness of skin tests in revealing drug allergy. The relevance of skin test results was evaluated with drug provocation studies.

METHODS: During 1989-2001, 947 patients with a history of suspected CADR were examined with skin tests including patch tests (PTs) (826 patients), skin prick tests (SPTs) (935 patients) and photopatch tests (12 patients). The occurrence of positive and negative test reactions to different drugs was correlated with clinical history. Drug provocation was carried out in 246 patients.

RESULTS: Antimicrobial drugs were suspected and tested most often. A positive PT reaction to one or more drug was seen in 89 of 826 (10.8%), most often to beta-lactams, clindamycin and trimethoprim. A positive SPT reaction was seen in 10 of 935 (1.1%) patients. Challenge was carried out in 17 patients with positive skin test results. Thirteen of 16 (81.2%) PT positives developed exanthema, three remained negative and one SPT-positive patient developed urticaria. Among skin test negatives, 207 of 229 (90.4%) challenges were negative and 22 of 229 (9.6%) were positive, 12 with exanthema, three with fixed drug eruptions and seven with urticaria.

CONCLUSIONS: Skin testing, especially the PT, was a useful screening method to find a cause of CADR if the reaction was exanthema and if antimicrobial, cardiovascular or antiepileptic drugs were suspected. The SPT detected occasional positives with antimicrobials. In cases of fixed drug eruption, PTs performed at the earlier reaction site were useful. When skin tests are negative or dubious, oral challenge should be carried out to confirm the association.