D1.85 - Basophil activation test in β-Lactam Anaphylaxis: A Case Series from a Tertiary Hospital

Self-reported β-lactam allergy prevalence in Europe ranges from 5% to 10%, while in vivo studies confirm only 1.5% to 6.1%. Cross-reactivity is driven by structural similarities in the β-lactam ring and shared side chains. β-lactam antibiotics are critical for treating bacterial infections. To identify the culprit drug to prevent unnecessary avoidance is essential, offer alternatives, and reduce antibiotic resistance risks. In vivo testing for severe hypersensitivity reactions is not risk-free, while the basophil activation test (BAT) represents a complementary in vitro tool, alongside specific IgE assays. We present a case series of BAT performance in β-lactam associated anaphylaxis.

Over three months, all drug allergy BATs performed in the immunology department of a tertiary hospital were analyzed. BATs followed EAACI guidelines, using commercially available extracts with dilutions in the recommended range. A positive result was defined as a stimulation index (SI) ≥ 2 and CD63 expression > 5%. Only β-lactam-related BATs were included, and data were analyzed using descriptive statistics.

β-lactam BATs accounted for 26.98% (17/63) of all tested drugs, involving 14 patients (41.18%) out of 34. The mean age was 45.36 years (SD 6.81, range 9–86), with 64.29% (N=9) male. All reactions were anaphylactic, with two (14.29%) cases of anaphylactic shock. Most reactions (64.29%, N=9) occurred during infection treatment, and 28.57% (4) were perioperative. BATs were performed within the first year of recovery in 71.43% (N=10) of cases. The distribution was as follows: 5 for ceftriaxone (29.41% suspected, confirmed once), 6 for amoxicillin-clavulanate (AX-CLV) (35.29% suspected, confirmed once), 3 for cefazolin (17.65% suspected, confirmed twice), and 1 each for cefoxitin, cefuroxime, and penicillin (all negative). Some other drugs were analyzed in parallel, but only propofol was identified as the culprit once.

The culprit drug was confirmed in 35.71% (5/14) of cases, including 4 β-lactams. β-lactam-induced anaphylaxis remains a significant concern, especially with cefazolin perioperatively and AX-CLV in hospitalized patients. The discrepancy between suspected and confirmed drug anaphylaxis may reflect misidentification with other non-allergic reactions. BATs with CD63 offer high specificity, though their sensitivity for β-lactams is debated. Combining CD203c may enhance diagnostic accuracy.