Interpretation of the Mantoux Test

Measurement and Classification of Test Results

The Mantoux test, also known as the tuberculin skin test (TST), is a diagnostic tool used to detect latent Mycobacterium tuberculosis infection.

Procedure

• A small amount of purified protein derivative (PPD) is injected intradermally into the forearm.
• The reaction is measured 48-72 hours post-injection.

Interpretation of Results

Measurement of Induration

The size of the induration (raised, hardened area) is measured, and its significance varies based on individual risk factors.

Classification Criteria

• ≥5 mm: Considered positive in immunocompromised individuals (e.g., HIV patients).
• ≥10 mm: Positive in those at increased risk (e.g., healthcare workers, recent immigrants).
• ≥15 mm: Positive in individuals with no known risk factors.

Limitations of the Mantoux Test

False positives can occur due to previous BCG vaccination, whereas false negatives may be seen in immunosuppressed individuals.

Next Steps and Confirmatory Tests

Positive results require further testing, such as chest X-rays or IGRA (interferon-gamma release assays), to confirm active tuberculosis.