3.9: Pulmonary Tuberculosis IV

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.

Diagnosing tuberculosis involves a series of tests.

The initial method is the Mantoux tuberculin skin test, which entails injecting a small amount of tuberculin-purified protein derivative intradermally into the forearm.

The development of a hard, raised bump known as induration within 48-72 hours may suggest a tuberculosis infection.

For individuals with HIV and those who have recently been in contact with tuberculosis patients, an induration of 5 millimeters or more is considered positive.

Regardless of risk factors, an induration of 15 millimeters or more is considered positive.

Next, interferon-gamma release assays involve blood tests that assess the immune system's response to Mycobacterium tuberculosis.

Additionally, a chest X-ray revealing upper lobe infiltrates, cavitations, or mediastinal lymphadenopathy can provide indications of pulmonary tuberculosis.

Sputum culture is used to identify the bacteria by collecting and cultivating a sputum sample in a laboratory.

Finally, CT or MRI can aid in the diagnostic process for detecting extrapulmonary tuberculosis.

• Tuberculosis (TB) – An infectious disease caused by Mycobacterium tuberculosis.
• Mantoux Test – A diagnostic tool primarily used to detect TB.
• Purified Protein Derivative (PPD) – A substance used in TB testing, specifically in the Mantoux test.
• Induration – A hard, raised bump, the size of which aids in TB diagnosis.
• Extrapulmonary TB – TB infection that affects body parts outside the lungs.

• Define Tuberculosis – Explain what it is (e.g., tuberculosis).
• Contrast Mantoux Test vs Other Diagnostic Tests – Explain key differences (e.g., Interferon Gamma Release Assays).
• Explore Induration Measurement - Describe scenario (e.g., interpretation based on risk factors).
• Explain the Process of TB Diagnosis – Short description of Mantoux test and other techniques.
• Apply Diagnosis in Context – Short description.

• [Question 1] What is Tuberculosis and how to diagnose it (include Mantoux test)?
• [Question 2] How is the size of induration relevant for TB diagnosis?
• [Question 3] What are the alternative diagnostic tests for TB?

• Students – Understand How the diagnosis of tuberculosis supports student understanding in medical studies
• Educators – Provides a clear framework it helps with teaching the topic of infectious diseases
• Researchers – Relevance for epidemiological study or improvement of diagnostic methods
• Healthcare Professionals – Broadens their knowledge of the different diagnostic tools for tuberculosis