Interobserver and method variability in tuberculin skin testing.

Accurate measurement and interpretation of tuberculin skin tests is essential both to avoid unnecessary prophylactic treatment with potentially hepatotoxic drugs and to ensure the proper institution of therapy in tuberculin-positive individuals. Although two methods are currently used for reading tuberculin skin tests, palpation and ballpoint, the optimal technique has not been established. We compared measurements obtained by each method on 101 patients tested with intermediate tuberculin purified protein derivative. Fifty-eight of these patients were also tested using Mono-Vacc. Excellent interobserver agreement among the five raters was demonstrated for both the palpation and ballpoint techniques. There was no significant difference between the two methods for any reader using the normal 10-mm cutoff point for a positive intermediate tuberculin purified protein derivative test. For any individual observer the decision as to whether the test was positive or negative was unaffected by the method in at least 93% of readings. We conclude that readings by physicians using palpation and ballpoint methods are comparable for clinical decision making.