An ultra-sensitive homologous chemiluminescence immunoassay to tackle penicillin allergy.

Penicillin is one of the most widely used antibiotics to treat bacterial infections in clinical practice. The antibiotic undergoes degradation under physiological conditions to produce reactive compounds that in vivo bind self-proteins. These conjugates might elicit an immune response and trigger allergic reactions challenging to diagnose due to the complex immunogenicity. Penicillin allergy delabeling initiatives are now part of antibiotic stewardship programs and include the use of invasive and risky in vivo tests. Instead, the in vitro quantification of specific IgE is highly useful to confirm immediate allergy to penicillins. However, discrepant results associated with the low sensitivity and accuracy of penicillin allergy in vitro tests have limited their routine diagnostic use for delabeling purposes. We aimed to develop a homologous chemiluminescence-based immunochemical method for the reliable determination of specific IgE to penicillin G, using unprecedented synthetic human-like standards. The synthetic standard targets the major antigenic determinant of penicillin G and the paratope of Omalizumab, acting as human-like specific IgE. It is a potent calibrator, highly stable, easy, and inexpensive to produce, overcoming the limitations of the pooled human serum preparations. The developed method achieved a good agreement and strong positive relationship, reaching a detection limit below 0.1 IU mL and excellent reproducibility (RSD <9%). The clinical sensitivity of the assay significantly increased (66%), doubling the accuracy of the reference method with an overall specificity of 100%. The new diagnostic strategy compares favorably with results obtained by the standard procedure, paving the way towards the standardization of penicillin allergy testing, and enhancing the detection sensitivity of specific IgE in serum to tackle reliably β-lactam allergy delabeling.