Immediate hypersensitivity to penicillins with negative skin tests--the value of specific IgE.

The determination of specific IgE in patients with history of penicillins hypersensitivity is simple, safe and widely available. The positive and negative predictive values of this determination, however, are not yet established. In order to evaluate them, we performed specific IgE determination and diagnostic drug challenges in a group of 22 patients with a clear history of immediate penicillins hypersensitivity but negative skin tests. In this sample, the positive and negative predictive values were 29% and 87%, respectively. This seems to indicate that a positive specific IgE is not enough to confirm the diagnosis, and further study is necessary.