Tuberculosis, more commonly referred to as TB, is an infectious disease stemming from Mycobacterium tuberculosis. While it primarily impacts the lungs, TB can also affect other body areas. Given its severity and global impact, timely and accurate diagnosis is crucial for controlling its spread and improving patient outcomes.
Several diagnostic approaches are used to detect TB. The conventional method is the Tuberculin Skin Test (TST), also known as the Mantoux test. However, this method has limitations as it cannot differentiate between latent TB infection and active TB disease. Furthermore, two visits to a healthcare facility are required for the test and results interpretation.
In the TST, a small amount of purified protein derivative (PPD) tuberculin is intradermally injected into the forearm. After 48 to 72 hours, the individual returns for examination, during which the healthcare provider measures the induration size, a hard, raised bump in millimeters, disregarding redness.
Interpretation of the TST results depends on induration size and the individual's risk factors for TB. A positive result (5 mm or more) is observed in individuals with HIV, recent TB contacts, those with chest radiographs consistent with prior TB, and patients with immunosuppressive conditions or organ transplants. Higher-risk groups, including recent immigrants from high TB prevalence countries, intravenous drug users, residents of high-risk settings, and children under four, consider an induration of 10 mm or more as positive. For individuals with no known risk factors, 15 mm or more is considered positive. The TST is a screening tool; a positive result prompts further testing to confirm active TB disease.
If an individual is experiencing symptoms of TB, it is crucial that healthcare providers perform other diagnostic tests immediately to ensure a timely and accurate diagnosis.
These additional diagnostic tests include Interferon Gamma Release Assays, which measure the immune system's response to TB bacteria; chest X-rays, which reveal lung damage; sputum culture, which cultivates TB bacteria from lung mucus; nucleic acid amplification testing, a rapid molecular test; and computer tomography (CT) or magnetic resonance imaging (MRI), which are crucial for detecting extrapulmonary TB.
