Prevalence of skin test reactivity in patients with convincing, vague, and unacceptable histories of penicillin allergy.

Penicillin (PCN) allergy has been vastly overdiagnosed, and too many people are incorrectly labeled as allergic to PCN, which affects their health by preventing the use of beta-lactam antibiotics. This investigation explores whether taking a careful history can eliminate the need for some to carry the PCN allergy label. A retrospective study of a focused history and PCN skin testing was done in a consecutive sample of a suburban allergy population of 319 patients who had a positive history of PCN allergy. The patients were divided into three groups based on PCN history: convincing, vague, and unacceptable. The convincing group had patients with impressive histories of PCN allergy likely to be immunoglobulin E-mediated. The vague group had unimpressive but plausible histories of PCN allergy. The unacceptable group were those patients with the PCN-allergic label who were either never exposed to PCN or the PCN reaction was too far-fetched to be believable. Out of 319 patients with a positive PCN allergy history, 135 (42.3%) patients were classified as convincing, 150 (47%) patients were classified as vague, and 34 (10.7%) patients were classified as unacceptable. Positive PCN skin tests were found in 19 of 135 (14.1%) patients in the convincing group, in 10 of 150 (6.7%) patients in the vague group, and 0 of 34 (0%) patients in the unacceptable group. The finding that 6.7% of patients with a vague PCN allergy history had positive skin tests suggests that skin testing is necessary in this group. The PCN-allergic label in the unacceptable group had been unchallenged by 33 primary care physicians and 9 allergists. This study suggests that physician acceptance of unwarranted PCN-allergic labels is not uncommon, and that such labels can be removed without skin testing.