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

Background: Allergic reactions to beta-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 beta-lactam allergy. Methods: The in vitro determination of beta-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((R))) 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 beta-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.