Tuberculose IV – Évaluation diagnostique

The Mantoux test, also called the Tuberculin Skin Test (TST), involves injecting a small amount of purified protein derivative (PPD) tuberculin intradermally into the forearm. After 48 to 72 hours, a healthcare provider examines the injection site and measures any hard, raised bump called induration in millimeters, disregarding redness. A positive result indicates possible tuberculosis infection and prompts further diagnostic testing.

Interpretation depends on induration size and TB risk factors. Individuals with HIV, recent TB contacts, or immunosuppressive conditions require 5 mm or more for a positive result. Higher-risk groups like recent immigrants need 10 mm or more. Those with no known risk factors require 15 mm or more. A positive TST is a screening tool that prompts further testing to confirm active TB disease.

The TST cannot differentiate between latent TB infection and active TB disease. Additionally, it requires two healthcare facility visits—one for injection and another 48 to 72 hours later for result interpretation. These limitations mean a positive TST alone is insufficient for diagnosis and necessitates additional diagnostic tests to confirm active tuberculosis.

Interferon Gamma Release Assays measure the immune system's response to Mycobacterium tuberculosis through blood tests. Chest X-rays reveal upper lobe infiltrates, cavitations, or mediastinal lymphadenopathy. Sputum culture identifies bacteria by cultivating lung mucus samples. Nucleic acid amplification testing provides rapid molecular detection. CT or MRI imaging detects extrapulmonary tuberculosis affecting areas beyond the lungs.

Chest X-rays reveal characteristic lung damage patterns associated with pulmonary tuberculosis, including upper lobe infiltrates, cavitations, or mediastinal lymphadenopathy. These radiographic findings provide strong indications of active TB disease. When combined with clinical symptoms and other diagnostic tests like sputum culture or interferon-gamma release assays, chest X-rays significantly support accurate TB diagnosis.

Sputum culture identifies Mycobacterium tuberculosis by collecting lung mucus samples and cultivating them in a laboratory. This test confirms the presence of TB bacteria and can provide information about drug resistance. Sputum culture is a definitive diagnostic method that, combined with chest X-rays and clinical assessment, establishes active TB disease and guides nursing management and prevention strategies.

CT or MRI imaging is crucial for detecting extrapulmonary tuberculosis, which occurs when TB affects areas beyond the lungs such as lymph nodes, bones, or the central nervous system. These advanced imaging techniques provide detailed visualization of affected tissues and help identify TB complications. They are particularly valuable when standard chest X-rays are inconclusive or when extrapulmonary involvement is suspected.