What kinds of tests are used to diagnose tuberculosis?

There are two kinds of screening tests for TB: the Mantoux tuberculin skin test (TST) and the blood test, called the interferon gamma release assay (IGRA).

For the TST, a healthcare provider will inject a small amount of a substance called purified protein derivative (PPD) under the skin of the forearm. After 2-3 days, the person must go back to the healthcare provider, who will look at the injection site. If the person has a TB infection, there will be a reddish lump.

For the IGRA, a healthcare provider will draw blood and send the sample to the lab.

Further tests to determine if an infection is active or if lungs are infected include:

How do I know if I should get tested for tuberculosis?

You should consider a TB screening test if:

  • You are a resident or employee in group settings where the risk is high (i.e., jails, hospices, skilled nursing facilities, shelters and other healthcare facilities).
  • You work in a mycobacteriology laboratory.
  • You have been in contact with a person who is known or suspected to have TB disease.
  • Your body's resistance to illness is low because of a weak immune system.
  • You think you might already have TB disease and are having symptoms.
  • You are from a country or lived in a country where TB disease is prevalent.
  • You have injected illicit drugs.

Others who are at risk for TB include:

  • People with immature or impaired immune systems, such as babies and children
  • People with kidney disease, diabetes, or other chronic (long-term) illness
  • People who have received organ transplants
  • People who are being treated with chemotherapy for cancer or other types of treatments for immune system disorders

The incidence rates for minority groups in the United States are higher than the incidence rates for whites.

Last reviewed by a Cleveland Clinic medical professional on 11/09/2018.


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