Interferon gamma release assay

Interferon gamma release assay (IGRA) is a medical test used to detect infection with Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB). The test measures the immune system's response to TB bacteria by testing the patient's blood for the presence of interferon gamma, a type of cytokine that is released by T cells in response to infection.

Etymology

The term "interferon gamma release assay" is derived from the function of the test. "Interferon gamma" refers to the specific cytokine that the test measures, while "release assay" refers to the method of testing, which involves measuring the amount of interferon gamma released by T cells in response to TB bacteria.

Procedure

The IGRA test involves drawing blood from the patient and incubating it with antigens (substances that trigger an immune response) derived from M. tuberculosis. If the patient's immune system has been exposed to TB bacteria, the T cells in the blood sample will release interferon gamma. The amount of interferon gamma in the sample is then measured to determine whether the patient has a TB infection.

Types of IGRA

There are two types of IGRA tests: the QuantiFERON-TB Gold In-Tube test (QFT-GIT) and the T-SPOT.TB test. Both tests are approved by the U.S. Food and Drug Administration (FDA) for the detection of TB infection.

Interpretation

A positive IGRA result indicates that the patient's immune system has been exposed to TB bacteria. However, it does not distinguish between latent TB infection (LTBI) and active TB disease. Additional tests are needed to confirm the diagnosis and determine the stage of the disease.

Advantages and Limitations

IGRA tests have several advantages over the traditional tuberculin skin test (TST), including greater specificity and the need for only one patient visit. However, they also have limitations, such as the inability to distinguish between LTBI and active TB disease, and the potential for false-positive results in patients who have been vaccinated with the Bacillus Calmette-Guérin (BCG) vaccine.

See Also

• Tuberculosis
• Mycobacterium tuberculosis
• Interferon gamma
• Cytokine
• T cells
• Antigen
• U.S. Food and Drug Administration
• Tuberculin skin test
• Bacillus Calmette-Guérin