The utility and interpretation of tuberculin skin tests in the Middle East

Tuberculin skin test (TST) interpretation can be confounded by Bacillus Calmette-Guérin (BCG) vaccination and infection with nontuberculosis mycobacteria (NTM). However, a wealth of epidemiologic information has allowed the formulation of recommendations for reasonably informed interpretation of the TST in most clinical situations. In the Middle East, the TST remains a useful test. BCG vaccination is given at birth, which should have minimal effect on TST reactions in adolescents or adults. In countries of the Middle East with moderate to high incidence of active smear-positive pulmonary TB (>20 per 100,000 per year), a positive TST will almost always indicate true TB infection. However, in Middle East countries with very low incidence of active TB (<10 per 100,000 per year), a positive TST will more likely be false positive because BCG vaccination is still routinely given; until BCG vaccination is abandoned, the TST will be less useful in these countries. These findings are applicable to countries in other regions of the world, and the utility TST will also be increased where the likelihood of TB infection is higher and lowered where TB infection is unlikely, yet BCG vaccination is still given.