TB Tests & Diagnosis

TB, which is short for tuberculosis, is a serious infectious disease caused by the mycobacterium tuberculosis bacteria. TB spreads when an infected person releases droplets into the air by coughing or sneezing. Physicians diagnose TB infections with various medical tests.

• Vintage TB Test Sign

Skin Tests

• Most physicians diagnose TB infections with the Mantoux skin test, which requires a small amount of PPD tuberculin to be injected just beneath the skin on the forearm. Infected patients typically develop a raised, red bump within 72 hours.

Culture Tests

• Doctors frequently take samples of sputum, which is the mucus that comes up when a patient coughs. Sputum culture tests help doctors prescribe the most effective medicines.

Other Tests

• Doctors commonly use blood tests to determine whether a TB infection is active or latent. Physicians might order a CT scan or a chest X-ray to determine the severity or location of a TB infection.

False-Positive Tests

• False-positive TB tests typically occur when a patient is infected with a non-TB type of mycobacterium. The bacillus Calmette-Guerin (BCG) vaccine sometimes causes false-positive test results.

False-Negative Tests

• Individuals with weakened immune systems, such as AIDS or chemotherapy patients, might not respond correctly to the Mantoux skin test. Vaccines that contain live viruses, such as smallpox and measles vaccines, often interfere with the accuracy of the Mantoux test.