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TB blood testing: Accurate, accessible, efficient

White Paper

read time: 3 minutes


Pathology & Laboratory Medicine

Tuberculosis (TB) testing is one of the cornerstones of keeping your workplace safe and your employees healthy. According to the Centers for Disease Control and Prevention (CDC), “more than 80% of the TB cases in the United States result from longstanding, untreated latent TB infection,”1 that is, from individuals who carry the TB bacterium, but show no symptoms for months or years after infection. Latent infections can be treated to remove the risk of symptomatic disease. More than 13 million Americans have latent TB infection,1 and testing is the only way to identify such individuals.

Because of TB’s high prevalence, high rate of latent infection, transmissibility, and impact on health from symptomatic infection, the CDC recommends TB screening and testing of all US healthcare personnel upon hire as part of a TB Infection Control Plan .2

The CDC also recommends that individuals who have been exposed to someone with symptomatic TB be evaluated for symptoms. Whether or not symptoms are present, those with a previous negative TB test should be tested immediately, and again 8 to 10 weeks after exposure. Those with a previous positive test need not be retested after exposure.

IGRA tests: Very high sensitivity and specificity with 1 office visit  

TB testing can be performed with the traditional less specific tuberculin skin test (TST), or with  improved blood testing options, including an interferon-gamma release assay (IGRA test). IGRA tests are more accurate, more time-efficient, and usually less costly than TSTs.

Similar to the TST, an IGRA test detects the cell mediated immune response by the release of interferon-gamma from white blood cells of a person who has been infected with TB, whether latent or symptomatic. Results in an IGRA test are read objectively, unlike the TST, which requires a subjective judgment of the skin reaction.

Quest offers 2 types of IGRA tests for TB:

  • T-Spot®.TB offers 95.6% sensitivity and 97.1% specificity and is approved for immunocompromised patients as well as the general population.3
  • QuantiFERON®-TB Gold Plus (QFT-Plus) offers 94% sensitivity and 97.1% specificity and delivers a more comprehensive evaluation of patients’ immune responses to TB.4

Both IGRA tests have lower rates of false positives compared to TST tests.3,4   Both T-Spot®.TB and QFT-Plus can be performed on a single tube of blood, and require only 1 office visit, unlike the TST, which requires the patient to return a second time to have the reaction read. And neither test is affected by the anti-TB bacillus Calmette–Guérin (BCG) vaccine, unlike the TST, which may register a false positive in vaccinated patients. IGRA tests are preferred by the CDC for TB testing in most risk groups versus TSTs.

Quest is committed to helping healthcare employers keep their employees and their community safe through timely, specific, and sensitive testing. Choosing the right test can offer employees both high accuracy and convenience in a single test.  

Page Published: March 30, 2023
  1. CDC. Latent TB Infection in the United States – Published Estimates. Accessed December 2, 2022.
  2. CDC. TB screening and testing of health care personnel. Updated August 30, 2022. Accessed December 2, 2022.
  3. T-SPOT®.TB. Package Insert. Oxford Immunotec; 2021. Accessed December 2, 2022.
  4. Qiagen. TB testing with QFT-Plus. Accessed December 2, 2022.
  5. USPSTF. Final recommendation statement: latent tuberculosis infection screening. Published September 6, 2016. Accessed December 2, 2022.