Recall antigen delayed-type hypersensitivity skin testing: standardization of self-reading by patients

In order to evaluate a self-reading system for the measurement of immunocompetence in cancer prognosis, a battery of delayed-type hypersensitivity skin tests with antigens including dermatophytin, candida, Varidase (streptokinase-streptodornase), mumps, and purified protein derivative (PPD) was administered to 50 cancer patients. The resulting erythema and induration were read by both technicians and patients at 24 and 48 h after placement of the tests. In addition, another group of 85 cancer patients received two identical candida skin tests placed at the same time on either the same or the opposite arm. The results from these two groups of patients indicated that patients' readings correlated well with technicians' readings, with most of the correlation coefficients being greater than 0.8. The weakest correlations were with antigens producing a large response. There was significant variability in the two identical simultaneously placed skin tests, and the correlation coefficients were much lower. The relevance of these data to serial skin testing is discussed.