The status of tuberculin skin testing at the Pahlavi University Medical Centre.

Thirty-four patients with tuberculosis were skin tested with 5 tuberculin units (TU) of purified protein derivative of Mycobacterium tuberculosis (PPD). PPD supplied by Park Davis and Co., Detroit, Michigan, U.S.A. (PPD-PD) as well as PPD obtained from The Razi Institute, Hessarak, Teheran (PPD-RI) were both used for skin testing in each patient. The results indicate that 74-79% of patients with active tuberculosis have positive tuberculin reactions, that PPD-RI is a potent source of tuberculin for skin testing and that a substantial proportion of our tuberculous patients (21-26%) have negative tuberculin skin reactions.