How Good Is the Tuberculin Skin Test?

Abstract

EXCERPT There may be nostalgia for the days when all tuberculin reactions meant tuberculous infection, and no nonsense.— Edwards and Edwards1 Purified protein derivative is a relatively crude material containing several different antigens. The results of a skin test with purified protein derivative are dependent on the immunologic reactivity of the recipient of the test, and the final interpretation is dependent on the individual interpreting the test. Despite these limitations, the tuberculin skin test (TST) is one of the most accurate medical tests available. Using conservative assumptions, I have estimated the sensitivity of the TST at approximately 95% and the specificity at approximately 99% to 99.5%.2 If these assumptions are correct, the TST is more accurate than most tests commonly used in clinical medicine.