Mantoux

The Mantoux tuberculin skin test (TST), commonly referred to as the Mantoux test, is a method for detecting infection with Mycobacterium tuberculosis. It uses an intradermal injection of purified protein derivative (PPD) tuberculin. A standard dose is 0.1 mL containing 5 tuberculin units (5 TU) injected into the inner forearm to produce a small raised wheel (wheal).

After 48 to 72 hours, the induration—the hard, raised area at the injection site—is measured in millimeters. The interpretation depends on risk factors and exposure history. Typical thresholds are: an induration of ≥5 mm is considered positive for high-risk individuals (e.g., people with HIV, recent TB contact, fibrotic changes on chest radiographs); ≥10 mm for medium-risk groups (e.g., recent immigrants from high-prevalence areas, IV drug users, residents or employees of high-risk settings, children under 4); and ≥15 mm for those with no known risk factors. A positive result indicates TB infection or exposure but cannot distinguish latent infection from active disease.

Limitations include false positives from prior Bacille Calmette-Guérin (BCG) vaccination or exposure to non-tuberculous mycobacteria, and false negatives in immunocompromised individuals, during the early window after infection, or in very young children. The Mantoux test requires a second visit for reading, and results must be interpreted in the clinical context alongside symptoms and radiographic findings.

History: The test was developed in 1908 by French physician Charles Mantoux, refining earlier tuberculin testing techniques. Today, TST remains in use in many settings, though interferon-gamma release assays (IGRAs) are used as alternatives or confirmatory tests in some populations.