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Penicillin allergy skin and blood tests have suboptimal accuracy

Published online: May 20, 2020

Patients reporting to be allergic to penicillins are at increased risk of antibiotic treatment failure and resistant infections. While up to 10% of Americans claim to be allergic to penicillins, only a minority of them has a true allergy. Therefore, clarifying whether a patient has a true penicillin allergy (or not) is of the utmost importance to ensure the prescription of the most adequate antibiotics. To do that, skin tests are frequently performed (sometimes preceded by blood tests), typically before challenging the patient with the suspected culprit drug in a controlled setting. However, there is still scarce information on the accuracy of such tests.

In a systematic review recently published in The Journal of Allergy and Clinical Immunology (JACI), Sousa-Pinto and colleagues observed that skin tests and blood tests (specific IgE quantification) have low sensitivity but high specificity. They collected data from 105 previously published studies comparing skin or blood tests with penicillin drug challenges - overall, the authors retrieved data from more than 30,000 patients reporting a penicillin allergy.  Data from the different studies were synthesized using meta-analysis methods, allowing authors to estimate the diagnostic properties of penicillin allergy skin tests and blood tests.

The researchers estimated that both skin tests and blood tests give negative results in more than 95% of individuals who do not have a true penicillin allergy. On the other hand, skin tests give positive results in only up to one-third of patients with true penicillin allergy, while for blood tests this proportion goes down to one-fifth. In addition, the authors projected that less than half patients with positive skin or blood tests have a true penicillin allergy.

Overall, penicillin allergy skin and blood tests have a suboptimal diagnostic accuracy, particularly in patients reporting mild non-immediate reactions. In clinical practice, a detailed clinical history may help in stratifying those patients who would benefit the most from those tests, and those who could safely undergo an allergist-supervised direct graded challenge with the suspected culprit penicillin.

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

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