Is p‐tert‐butylphenol‐formaldehyde resin (PTBP‐FR) in TRUE Test® (Mekos test) sensitizing the tested patients?

BACKGROUND: In a population study using TRUE Test®, we noted late reactions to p-tert-butylphenol-formaldehyde resin (PTBP-FR) in 0.5% of subjects tested. OBJECTIVES: In order to explore possible test sensitization, differences in the contents of sensitizers within PTBP-FR in test preparations for TRUE Test® and Finn Chambers® were analysed. Subjects allergic to PTBP-FR and subjects with late reactions to PTBP-FR were retested in order to explore whether these groups reacted to different PTBP-FR sensitizers. PATIENTS/MATERIALS/METHODS: Four individuals with late reactions and 5 subjects with established allergy to PTBP-FR were retested with defined PTBP-FR sensitizers. PTBP-FR constituents in patches from TRUE Test® were analysed with high-performance liquid chromatography. Previously analysed samples of PTBP-FR constituents served as a reference. RESULTS: The pattern of reaction to PTBP-FR sensitizers was similar in both groups. Subjects with suspected sensitization had somewhat stronger reactions than controls. The concentrations of monomers, dimers and trimers were generally higher in the TRUE Test® resin than in reference substances. CONCLUSIONS: Retesting did not add information regarding causes of possible sensitization. Analysis showed that the resin used in TRUE Test® has a lower degree of polymerization or condensation, which may enhance its sensitizing properties. A follow-up of late reactions to PTBP-FR in TRUE Test® should be carried out.