The role of skin testing for penicillin allergy.

Skin testing for penicillin allergy is an imperfect predictor of severe allergic reactions. We used decision analysis to identify the types of allergy history for which skin testing should alter management. The treatment threshold, the probability of a serious allergic reaction at which point one should switch from penicillin to another antibiotic, depends on the quality of life associated with the clinical outcomes. We measured 12 physicians' attitudes toward the outcomes of treatment with penicillin or vancomycin for Streptococcus viridans endocarditis in patients with a history of penicillin allergy. The clinicians' threshold probabilities ranged from .00010 to .00210 (median, .00013). Given the sensitivity (89% to 96%) and specificity (89% to 96%) of skin testing and our clinicians' median threshold, test results could alter the choice of antibiotic when the probability of a severe allergic reaction is between .00001 and .001. This range corresponds to a weak history of penicillin allergy. Although the decision should be individualized, our study suggests that skin testing is unnecessary when the patient has a convincing history of a severe allergic reaction to penicillin.