Tin Sum Li,1* Harris K.S. Hui,1* Andy Ka Chun Kan,1* Maegan H.Y. Yeung,1 Jane C.Y. Wong,1 Valerie Chiang,2 Philip Hei Li1

Affiliations:
1 Division of Rheumatology and Clinical Immunology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong
2 Division of Clinical Immunology, Department of Pathology, Queen Mary Hospital, Hong Kong

*Tin Sum Li, Harris K.S. Hui and Andy Ka Chun Kan contributed equally to this work and should be considered joint first author

Abstract

Background: Incorrect penicillin ‘allergy’ labels predispose patients to adverse outcomes but are under-recognised in many Asian countries. Studies on performance and post-delabelling outcomes of penicillin allergy evaluation among Chinese remain scarce.
Objective: To evaluate the diagnostic performance of allergy testing and post-delabelling outcomes among Chinese patients in a prospective penicillin allergy cohort – Prospective Assessment of Penicillin Allergy (PAPA).
Methods: All adult patients (age ≥ 18 years) who underwent penicillin allergy evaluation between January 2020 to December 2021 were recruited and prospectively reviewed by both medical records and individual interviews at least 6 months after delabelling or allergy confirmation.
Results: Out of 372 patients who completed penicillin allergy evaluation, 335 (90%) patients were delabelled. The overall negative predictive value of penicillin skin testing was 95%, but lower for patients with non-immediate type reactions (88%). History of non-immediate symptom onset (OR = 4.501 [95%CI = 2.085-9.716], p < 0.001) and duration since index reaction (OR = 0.942 [95%CI = 0.899-0.987], p = 0.012) were associated with positive skin testing. After at least 6 months, 60 (18%) of de-labelled patients had received penicillins again without any adverse reactions. Fluoroquinolone-use was significantly lower among delabelled patients compared to those with penicillin allergy (38[11%] vs 11[30%], p = 0.004).
Conclusion: After at least 6 months, one in six delabelled patients already received penicillins again safely,
with significantly lower fluoroquinolone usage. None experienced adverse reactions. History of non-immediate onset and shorter duration since index reaction were associated with genuine allergy. In patients with severe non-immediate reactions, skin tests should be supplemented with thorough clinical history and adjunct diagnostic evaluations.
Key words: Allergy, Penicillin, Delabelling, Outcome, Prospective Study