Tuberculin Skin Test (Mantoux Test) for TB

Tuberculin Skin Test

• A positive result is indicated by a delayed hypersensitivity reaction, evident 48-72 hours after intradermal injection of purified protein derivative (PPD), resulting in a raised, indurated lesion >6 mm diameter in non-vaccinated adults.
• In bacille Calmette-Guérin (BCG)-vaccinated adults, a positive result is indicated by a raised, indurated lesion >15 mm.
• False-negative results can occur in immunosuppressed individuals, such as those with HIV infection, sarcoidosis, or taking certain medications, and at the extremes of age or in active disease.
• False-positives can occur due to cross-reactivity with non-tuberculous mycobacteria and BCG Vaccine.

Interferon-Gamma Release Assays (IGRAs)

• IGRAs detect T-cell secretion of IFN-γ following exposure to M.tuberculosis-specific antigens (ESAT-6, CFP-10).
• The test does not differentiate between active and latent infection.
• IGRAs have high specificity compared to the TST and similar or better sensitivity, requiring only a single visit.

Microbiological Diagnosis

• Serial sputum samples should be collected on at least three occasions, ideally immediately upon waking.
• Bronchoscopy and lavage can be used to obtain respiratory secretions.
• Auramine-rhodamine staining is more sensitive (though less specific) than Ziehl-Neelsen staining, and is widely used.
• Auramine-rhodamine staining requires fluorescence microscopy and highlights bacilli as yellow-orange on a green background.
• Mycobacterial culture can be done using liquid/broth culture (1-3 weeks) or solid media (Lowenstein-Jensen slopes or Middlebrook agar) (3-8 weeks).

Tuberculin Skin Test

• A positive result is indicated by a delayed hypersensitivity reaction, evident 48-72 hours after intradermal injection of purified protein derivative (PPD), resulting in a raised, indurated lesion >6 mm diameter in non-vaccinated adults.
• In bacille Calmette-Guérin (BCG)-vaccinated adults, a positive result is indicated by a raised, indurated lesion >15 mm.
• False-negative results can occur in immunosuppressed individuals, such as those with HIV infection, sarcoidosis, or taking certain medications, and at the extremes of age or in active disease.
• False-positives can occur due to cross-reactivity with non-tuberculous mycobacteria and BCG Vaccine.

Interferon-Gamma Release Assays (IGRAs)

• IGRAs detect T-cell secretion of IFN-γ following exposure to M.tuberculosis-specific antigens (ESAT-6, CFP-10).
• The test does not differentiate between active and latent infection.
• IGRAs have high specificity compared to the TST and similar or better sensitivity, requiring only a single visit.

Microbiological Diagnosis

• Serial sputum samples should be collected on at least three occasions, ideally immediately upon waking.
• Bronchoscopy and lavage can be used to obtain respiratory secretions.
• Auramine-rhodamine staining is more sensitive (though less specific) than Ziehl-Neelsen staining, and is widely used.
• Auramine-rhodamine staining requires fluorescence microscopy and highlights bacilli as yellow-orange on a green background.
• Mycobacterial culture can be done using liquid/broth culture (1-3 weeks) or solid media (Lowenstein-Jensen slopes or Middlebrook agar) (3-8 weeks).

This quiz covers the Tuberculin Skin Test, also known as the Mantoux test, used to diagnose tuberculosis (TB). Learn how to interpret the results, including the measurement of the raised, indurated lesion in non-vaccinated and vaccinated adults.