Rapid Sputum Tests for Tuberculosis (TB)

Topic Overview

Rapid sputum tests are used to diagnose tuberculosis (TB) when other tests show that a person probably has TB. Rapid sputum tests are also called nucleic acid amplification tests (NAAs).

One of the best ways to diagnose TB is through a sputum culture. A sputum culture is a test to find germs (such as TB bacteria) that can cause an infection. A sample of sputum is added to a substance that promotes the growth of bacteria. If no bacteria grow, the culture is negative. If bacteria grow, the culture is positive. If TB bacteria grow, then the person has tuberculosis. The test also can show if a lung infection is caused by some other kind of bacteria. A sputum culture can take 1 to 8 weeks to provide results.

Rapid sputum tests can tell if a person has TB within 24 hours. A test may be done when:^{footnote 1}

• A person is thought to have TB, but confirmation is needed before sputum culture results will be ready.
• A person may be infected with bacteria other than TB bacteria.
• A person who may have TB has been close to other people who will need treatment if they have been exposed.