At present, two different test methods may be used to determine the TB status of the patient. An immune response is usually best determined after 2-10 weeks post-exposure.
1. Tuberculin skin test (TST)
2. Blood tests (interferon-gamma release assays [IGRA])
One or both tests may be used. Interpreting the results of laboratory blood tests in combination with the skin test result is valid. However, according to the CDC, a TST and TB blood test is not recommended.
In certain circumstances, results from both tests might be helpful when:
- ...the initial test is negative, and the risk for progression to TB disease or a poor outcome (HIV-infected) is high, or clinical suspicion is high (positive radiology).
- ...the initial test is positive, and the individual has a history of BCG vaccine, or the individual is at low risk of progression from infection to disease.
