Tuberculosis (TB) Test Overview

A tuberculosis (TB) test is performed to detect infection caused by Mycobacterium tuberculosis, the bacteria responsible for TB. This infectious disease primarily affects the lungs but can also spread to other organs such as the brain, kidneys, or spine. TB spreads through the air when an infected person coughs, sneezes, or speaks, making early detection vital for both patient care and public health.

Testing helps determine whether a person has a latent TB infection (bacteria present but inactive) or active TB disease, which is contagious and requires immediate treatment. By diagnosing TB early, doctors can prevent complications, reduce the risk of spread, and begin appropriate therapy as soon as possible.

A TB test in Bangalore can vary in cost depending on the type of test needed.

Why Is the Test Prescribed?

Doctors may recommend a TB test in the following situations:

• Symptoms suggestive of TB such as persistent cough lasting more than two weeks, chest pain, unexplained fever, night sweats, or sudden weight loss.
• Close contact with someone already diagnosed with active TB.
• High-risk groups including individuals with weakened immune systems (e.g., HIV-positive patients), healthcare workers, or those living in crowded conditions.
• Before starting certain medicationsparticularly immunosuppressants, which may trigger latent TB to become active.
• Monitoring treatment progress in individuals already on anti-TB therapy.

Types of TB Tests

Several diagnostic methods are available to detect TB infection:

• Tuberculin Skin Test (TST / Mantoux Test) - A small amount of tuberculin is injected just under the skin of the forearm. The reaction is measured after 48–72 hours. A raised bump or swelling indicates possible TB exposure
• Interferon-Gamma Release Assays (IGRAs) – A blood test that measures the immune system’s response to TB bacteria. It is more specific than the skin test and requires only one visit.
• Sputum Test – – In suspected active TB cases, sputum samples are examined for TB bacteria using microscopy, culture, or molecular tests such as GeneXpert.
• Chest X-ray –Frequently recommended to check for lung damage or signs of active TB disease.

Doctors often combine these methods for accurate diagnosis.

Procedure and Prerequisites

The procedure depends on the type of test performed:

• Skin Test:A small injection is placed under the skin; no fasting is needed. The result must be checked by a healthcare professional after 48–72 hours.
• Blood Test (IGRA):A routine blood sample is taken from a vein; no special preparation is required. Results are generally available within 1–2 days.
• Sputum Examination: Patients may need to provide one or more early morning sputum samples.
• Chest Imaging: Performed quickly without any preparation requirements.