Validation of self-testing as a method to estimate the prevalence of nickel allergy. 
The aim of this study was to investigate the validity of self-patch testing for nickel allergy, in order to determine a cost-effective method for surveillance of the prevalence of nickel allergy.  Population-based study including patch testing is the most reliable method to study the prevalence of allergy, but it is expensive and has logistical problems.  A total of 191 dermatology patients referred to patch testing were provided with a self-test package with written instructions.  The self-test was applied on the arm by the patient, on the same day that the regular patch test was applied on the back.  The patient evaluated the self-test before patch test reading at the clinic.  Patch test at the dermatology clinic detected 46/191 (24%) nickel-positive individuals.  The sensitivity of the self-test was 72% (95% confidence interval (CI) 57-84), the specificity 91% (95% CI 85-95), and the proportion of agreement 86% (95% CI 81-91).  Thus, in the population studied, the validity of self-testing for nickel allergy was adequate.