Why do tb test

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Last updated: April 8, 2026

Quick Answer: Tuberculosis (TB) tests are performed to detect Mycobacterium tuberculosis infection, which causes TB disease. The World Health Organization reported 10.6 million new TB cases globally in 2022, with 1.3 million deaths. Testing is crucial because TB is a leading infectious disease killer worldwide, and early detection allows for effective treatment with antibiotics like isoniazid and rifampin. The most common tests are the tuberculin skin test (TST), developed in the early 1900s, and interferon-gamma release assays (IGRAs), introduced in the 2000s.

Key Facts

10.6 million people fell ill with TB globally in 2022
TB caused 1.3 million deaths in 2022
Tuberculin skin test (TST) was developed by Charles Mantoux in 1907
Interferon-gamma release assays (IGRAs) were approved by the FDA in the early 2000s
Standard TB treatment involves 6-9 months of antibiotics

Overview

Tuberculosis (TB) testing is essential for diagnosing infection with Mycobacterium tuberculosis, the bacterium that causes TB disease. TB has plagued humanity for millennia, with evidence found in Egyptian mummies from 2400 BCE. In the 19th century, TB was called "consumption" and was a leading cause of death in Europe and America. Robert Koch identified the causative bacterium in 1882, revolutionizing understanding. The tuberculin skin test (TST) was developed by Charles Mantoux in 1907, using purified protein derivative (PPD) from TB bacteria. Today, TB remains a major global health threat, particularly in developing countries and among immunocompromised individuals. The World Health Organization's End TB Strategy aims to reduce TB deaths by 95% by 2035 compared to 2015 levels.

How It Works

TB tests detect immune responses to Mycobacterium tuberculosis. The tuberculin skin test (TST) involves injecting 0.1 ml of PPD tuberculin into the forearm's inner layer. After 48-72 hours, a healthcare provider measures any induration (hard swelling); 5 mm or more indicates infection in high-risk groups, while 15 mm or more is positive for low-risk individuals. This test relies on delayed-type hypersensitivity. Interferon-gamma release assays (IGRAs), such as QuantiFERON-TB Gold and T-SPOT.TB, are blood tests that measure T-cell release of interferon-gamma when exposed to TB-specific antigens. IGRAs are more specific than TST because they use antigens not found in BCG vaccine strains, reducing false positives. Both tests identify latent TB infection, which requires further evaluation (like chest X-rays) to confirm active disease. Newer methods include molecular tests like Xpert MTB/RIF, which detects TB DNA and rifampin resistance in sputum within hours.

Why It Matters

TB testing matters because early detection saves lives and prevents transmission. Active TB disease can spread through airborne droplets when an infected person coughs or sneezes. Without treatment, TB has a high mortality rate. Testing high-risk populations—such as healthcare workers, immigrants from high-incidence countries, and people with HIV—helps control outbreaks. In 2022, the WHO estimated that TB testing and treatment averted 75 million deaths since 2000. However, drug-resistant TB strains pose challenges, with about 410,000 cases of rifampin-resistant TB in 2022. Testing enables targeted antibiotic therapy, reducing the risk of resistance development. Public health programs rely on testing data to allocate resources and track progress toward elimination goals.