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. It is useful to be able to interpret the results of laboratory blood tests in combination with the skin test result. However, according to CDC, the use of both a TST and TB blood test is not recommended.
In certain circumstances, results from both tests might be useful 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.
