Reproducibility of Patch Test Reactions and Interpretation of Doubtful Results: A Retrospective Study of Identical Haptens Tested Simultaneously in Different Series
Norbertus A. Ipenburg, Anton C. de Groot, Thomas RustemeyerABSTRACT
Background
Reproducibility of patch test reactions remains debated, and the clinical significance of doubtful (?+) reactions is unclear.
Objectives
To evaluate reproducibility of positive reactions to identical haptens tested simultaneously in different series and analyse doubtful reactions using paired co‐reactivity patterns.
Materials and Methods
Patch test data from consecutive patients tested during 2015–2025 were analysed retrospectively. Six haptens were evaluated at standard concentrations in petrolatum: hydroxyisohexyl 3‐cyclohexene carboxaldehyde (Lyral, HICC) 5% pet., Amerchol L‐101 50% pet., lanolin alcohol 30% pet., hydroxyethyl methacrylate (HEMA) 2% pet., mercaptobenzothiazole (MBT) 2% pet. and
Results
Reproducibility was hapten‐dependent. HEMA and MBT showed substantial to almost perfect agreement. HICC showed substantial agreement but a significantly higher positivity rate in the perfume series than in the baseline series. Amerchol L‐101, lanolin alcohol and MPR showed lower positive agreement and fair‐to‐moderate kappa values. Most doubtful reactions were isolated, particularly for Amerchol L‐101 and lanolin alcohol, whereas 43.8% of doubtful HICC reactions in the baseline series were supported by perfume‐series reactivity.
Conclusions
Reproducibility was strongly hapten‐dependent. In this dataset, paired co‐reactivity provided clinical context for interpreting discordant positive and doubtful reactions.