Relevance of the determination of serum‐specific IgE antibodies in the diagnosis of immediate β ‐lactam allergy

Background:  Allergic reactions to β ‐lactams are the most frequent cause of adverse drug reactions mediated by specific immunologic mechanisms. They can be explored by in vivo and/or in vitro tests. The measurement of serum‐specific immunoglobulin E (IgE) presents several advantages: safety, simplicity, and availability to nonallergologist physicians. Objectives:  To establish the diagnostic value of specific IgE determination in the diagnosis procedure of immediate β ‐lactam allergy. Methods:  The in vitro determination of β ‐lactam‐specific IgE antibodies was compared in three well‐defined groups of patients ( n  = 45): one with negative skin tests and a positive drug provocation test, another with positive skin tests, and a third control exposed population with good tolerance. Two techniques were used: the CAP‐FEIA system (Phadia ® ) commercially available and a homemade radioallergosorbent test (RAST). Results:  The specificity of CAP‐FEIA ranged from 83.3% to 100% and sensitivity from 0% to 25% depending on initial clinical manifestations. The specificity of RAST was between 66.7% and 83.3% and sensitivity 42.9% and 75%. In the subgroup of patients with an anaphylactic shock and negative skin tests, the sensitivity and specificity of RAST were 75%. Positive and negative predictive values were 45.5% and 77.1% with CAP‐FEIA and 38.5% and 81.5% with RAST, respectively. Conclusion:  These results indicate that, although the specificity of β ‐lactam‐specific IgE measurement is good, sensitivity is low. Immunoglobulin E measurement should be limited to patients with a clinical history of anaphylactic shock and negative skin tests in order to avoid a drug provocation test. More sensitive assays should be developed.