Tuberculosis Ag, IFN-gamma response refers to the summary interpretation of an IGRA test that is used to investigate whether the immune system reacts to specific antigens from bacteria within the Mycobacterium tuberculosis complex.
The analysis is immunological and does not detect the tuberculosis bacterium itself in the blood. Instead, it examines how the immune system's T lymphocytes react when exposed to tuberculosis-specific antigens in the laboratory. If the body has previously been in contact with tuberculosis, the T cells can recognize these antigens, become activated and release interferon-gamma, IFN-γ. The amount of interferon-gamma is then measured as a sign of the immune system's reaction to the tuberculosis antigen.
IGRA is based on the immunological response of T cells
Interferon-gamma is a cytokine, i.e. a signaling molecule that has a central role in the cell-mediated immune system. When specific T cells recognize tuberculosis antigens, they can be activated and release interferon-gamma. This release is measured in the laboratory and is used as an indirect measure of whether the immune system has previously reacted to tuberculosis antigens.
The analysis is therefore based on immunological memory and differs from microbiological methods that directly attempt to detect the bacterium or bacterial genetic material.
The summary interpretation is based on the entire analysis
The IGRA analysis includes, among others, Tuberculosis Ag 1, TB1, and Tuberculosis Ag 2, TB2. Both measure interferon gamma response after stimulation with tuberculosis-specific antigens, but they are designed to stimulate slightly different T-cell populations.
TB1 stimulates primarily CD4+ T-cells, while TB2 stimulates both CD4+ and CD8+ T-cells. Both results are analyzed together with the analysis's control values before the laboratory provides a summary interpretation.
The result is reported as positive, negative or not assessable
The final assessment is stated as positive, negative or not assessable. A positive result means that the assay has shown an immunological response to the tuberculosis-specific antigens included in the test. A negative result means that no clear such response has been demonstrated. A result stated as not assessable means that the assay control values or other measurement results do not allow a reliable interpretation.
TB1 and TB2 are reported separately
In addition to the summary interpretation, Tuberculosis Ag 1 and Tuberculosis Ag 2 are reported as separate quantitative IFN-gamma responses in IU/mL. These values are subcomponents of the assay and should not be interpreted as independent diagnostic markers.
It is the combined assessment of TB1, TB2 and the control samples that forms the basis for the laboratory's final IGRA response.
IGRA shows immunological reactivity but not disease activity
A positive IGRA result shows that the immune system has reacted to tuberculosis-specific antigens. The result may indicate tuberculosis infection, but the test alone cannot determine whether the infection is latent or whether the person has active tuberculosis disease.
If active tuberculosis is suspected, other targeted diagnostics and medical assessment are therefore required. IGRA primarily serves as an immunological support and should always be evaluated together with other clinical information.
