TB Quantiferon (IGRA)

The Interferon Gamma Release Assay (IGRA) is recommended for people at high risk for tuberculosis (TB) infection or disease. This includes

- Healthcare workers: Healthcare workers are at increased risk for TB due to frequent exposure to patients with the disease.
- Immigrants from high-prevalence countries: People who have immigrated from high-prevalence countries, such as India, China, and Mexico, are at increased risk for TB.
- People with HIV/AIDS: HIV weakens the immune system and increases the risk of developing active TB disease.
- Close contacts of people with active TB disease: People who have been in close contact with someone who has active TB disease are at increased risk of infection.

IGRA may also be recommended for

- People who have received the Bacille Calmette-Guérin (BCG) vaccine: The BCG vaccine can cause false-positive results with the traditional TB skin test, but not with the IGRA. Therefore, IGRA is recommended for people who have received the BCG vaccine.
- People who cannot return for a second appointment: The traditional TB skin test requires two appointments, while the IGRA requires only one blood draw. Therefore, IGRA may be more convenient for people who cannot return for a second appointment.

Note that not everyone needs to be tested for TB infection or disease. Your healthcare provider can help determine if you are at increased risk and whether testing is necessary.

Interferon gamma release assay (IGRA) test results are reported as positive, negative, or indeterminate. Interpretation of the test results is based on the amount of interferon-gamma released or the number of cells releasing interferon-gamma. Both the standard qualitative test interpretation and the quantitative assay measurements should be reported.

- Positive result: A positive result indicates that M. tuberculosis infection is likely. The cutoff for a positive result varies depending on the specific IGRA assay used, but generally ranges from 0.35 to 0.7 IU/mL for interferon-gamma concentration or 6 to 10 spot-forming cells (SFCs) per well for spot count.
- Negative result: A negative result indicates that M. tuberculosis infection is unlikely. However, a negative result does not completely rule out TB infection, especially in people with weakened immune systems.
- Indeterminate result: An indeterminate result means that the test could not give a clear answer due to technical problems or problems with the blood sample. Indeterminate results can occur in up to 10% of tests and may require retesting.

You should be aware that multiple negative results from any combination of TB tests cannot rule out M. tuberculosis infection, especially in people with ongoing exposure or symptoms suggestive of TB disease.

Your healthcare provider will interpret your IGRA test results along with other clinical information and may recommend further testing or treatment as needed.