Diagnosis of immediate reactions to amoxicillin: Comparison of basophil activation markers CD63 and CD203c in a prospective study.

BACKGROUND: Amoxicillin (AX) combined or not with clavulanic acid (CLV) is frequently involved in IgE mediated reactions. Drug provocation test (DPT) is considered as the gold standard for diagnosis, although contraindicated in high-risk patients. Basophil activation test (BAT) can help diagnose immediate reactions to betalactams, although, controversy exists regarding the best activation marker. We have performed a real-life study in a prospective cohort to analyse the real value of BAT as diagnostic tool and the best activation marker, CD63 and CD203c, for the evaluation of immediate reactions to these drugs.

METHODS: We prospectively evaluated patients with a clinical suspicion of immediate reactions after AX or AX-CLV administration during a 6-years period. The allergological workup was done following the EAACI recommendations. BAT was performed in all patients using CD63 and CD203c as activation markers.

RESULTS: In AX allergic patients, both activation markers, CD63 and CD203c, showed similar SE values (48.6% and 46.7% respectively), however specificity was of 81.1% and 94.6% respectively, with CD203c showing with good positive predictive value and like-hood ratio. In CLV allergic patients, CD203c showed higher SE (50%) than CD63 (42.9%), maintaining the same value of SP (80%). Combining results of both markers can slightly increase the sensitivity (51.4% for AX and 54.8% for CLV), although decreasing the specificity (79.7% and 73% respectively). Interestingly, all patients with an anaphylactic shock showed a positive BAT to CLV using CD203c.

CONCLUSIONS: BAT using CD203c showed a good confirmatory power, especially for AX allergy. Placing BAT as a first step in the diagnostic procedure can help reduce the need of performing a complete allergological-work up in a 46.6% of patients, diminishing the risk of re-inducing allergic reactions.