To the Editor.
—Despite the obvious importance of proper interpretation of the PPD and other delayed hypersensitivity skin testing, it has been our impression that physicians' criteria for interpretation are variable. To assess the standards being used to interpret delayed hypersensitivity skin testing, a questionnaire was sent to attending physicians, medical house officers, and medical students. In addition, a retrospective chart review also was conducted to assess the degree of documentation of skin test results recorded in the medical record.A total of 129 of 257 questionnaires were returned. The majority of respondents (112/129) defined a positive intermediate PPD skin test as having a diameter of induration equal to or greater than 10 mm. In contrast to the uniformity of criteria for a positive PPD skin test, the other skin tests (mumps, Candida, streptokinase-streptodornase, and Trichophyton) were interpreted by a wide range of criteria: 28%, 5- to 9-mm induration; 44%,