Patch-Test Sensitivity and Reproducibility in Individuals and Populations

Abstract

Problems of patch testing discussed are the understanding and methodology of testing in individual patients and the application of opidomiological methods to populations. 1. Delayed immune sensitivity is dose-related, not an all-or-none phenomenon, and a positive patch test is a reflection of a relatively gross phase of sensitization. Thus, a positive patch test indicates sensitization, but a negative test does not prove its absence. Therefore, patch testing should incorporate a dose response. Independent allergens and irritants summate in patch tests. This explains negative patch tests in truly sensitive patients and the “false-positive” reactions of the “angry back”. Response can now be measured objectively; the subjective response should be regraded to include a +++++. 2. Poor statistics and epidemiology explain much of the reported population variation. Common problems are: too small of a sample size, too small a period of study (units of a year are desirable), as well as control of age, sex, occupation, and usage. However, the most important error is poor definition of the clinical reference base; unless individuals are studied consecutively or randomly from a tightly defined clinical reference base, the prevalence found will not be applicable to other situations. In summary, improved use of a dose response, the objective measurement of response, and the use of summating patches, together with a more sophisticated approach to epidemiology, would improve what is otherwise a powerful and useful clinical methodology.