Tuberculin skin testing: Indication, interpretation, and management

PURPOSE: To review the indication, interpretation, and management of tuberculin skin testing (TST) in a case-based format. EPIDEMIOLOGY: Worldwide, tuberculosis (TB) is the second most common cause of death among infectious diseases. An estimated 10% of the 10 to 15 million persons with latent tuberculous infection (LTBI) will develop active disease at some point in life if they are not treated. REVIEW SUMMARY: Despite the continuing decline in the reported cases of active TB, a significant reservoir of individuals infected with Mycobacterium tuberculosis is expected to be the source of new cases of active TB. The highest priority of a targeted tuberculin testing program is to identify persons at increased risk for TB who will benefit from treatment for LTBI. TST remains the primary diagnostic and screening test for LTBI. Three different cut-off values have been chosen for interpretation of size in TST results depending on estimated risk of acquisition of M tuberculosis and the risk of developing active disease. TYPE OF AVAILABLE EVIDENCE: Nationally recognized treatment guidelines, prospective cohort study, meta-analysis, unstructured review. GRADE OF AVAILABLE EVIDENCE: Good. CONCLUSION: TST is still a valuable tool for the diagnosis of patients with LTBI. Interpretation of TST results depends not only on the size or reaction, but also on its predictive value as well as on the risk of developing the disease. The decision to test for TB means the decision to treat people who have positive TST results.