Frequency of Negative Intermediate-Strength Tuberculin Sensitivity in Patients with Active Tuberculosis

Abstract

Abstract One hundred and fifteen consecutive patients with documented active tuberculosis were skin-tested with three different tuberculin preparations, each of which reportedly contained 5 Tuberculin Units (5 TU) of purified protein derivative (PPD). A surprising lack of uniformity was demonstrated. Commercial antigen (PPD-PD) was associated with negative (0 to 4 mm) reactions in 49 per cent and doubtful (5 to 9 mm) reactions in 10 per cent of these patients. Purified protein derivative standard (PPD-S) gave 34 per cent negative and 3 per cent doubtful reactions. PPD stabilized with Tween-80 resulted in negative reactions in 17 per cent and doubtful reactions in 2 per cent of patients. A major factor in these false and nonpositive results appears to be loss of potency of the antigen through adsorption. Nonstabilized preparations are probably delivering less antigen than stated by the manufacturer, and this point is of great importance at low doses (i.e., 5 TU).