Quantiferon tb gold test

Synonym(s)

IGRA; Interferon gamma release assay

Definition
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Highly sensitive immunological test for tuberculosis screening. The tuberculosis-specific antigens ESAT-6 (early secretory antigen target-6), CFP-10 (culture filtrate protein 10) and TB 7.7 (p4) are used, which are only found in M. tuberculosis and M. bovis. These antigens are absent in all strains used for BCG vaccines and in most non-tuberculous mycobacteria (atypical mycobacteria) except M. kansasii, M. marinum, M. szulgai and M. flavescens. The interferon-γ formation of T-effector cells stimulated with the above-mentioned antigens specific for M. tuberculosis is detected.

General information
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The sensitivity of this test system is stated to be about 90% (for comparison tuberculin skin test: < 70%) with a specificity of 98%. In addition, the general stimulability of T-lymphocytic IFN-γ formation is investigated to prevent false negative test results. In this way, a statement regarding the T-cell-mediated immunity situation is also possible.

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Indication
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Environmental investigation of contact persons in proven cases of open TB.
Screening of healthcare workers for previous TB infection.
Detection of active tuberculosis before starting immunosuppressive therapy, e.g. when using biologicals or methotrexate for the treatment of psoriasis and rheumatic diseases.
Screening of immunosuppressed patients taking into account the number of CD4 cells.

Note(s)
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The test tubes are coated with a combination of these antigens that stimulate the T cells in the patient's whole blood sample. Upon prior contact with M. tuberculosis, the T cells release interferon-γ into the plasma. Interferon gamma is measured by ELISA tests. This is used to assess the probability of TB infection.
Notice!
The test is not affected by a previous BCG vaccination. Considering the controls, the test can also be used in patients with immunodeficiency (e.g. HIV).
For this test, special collection tubes are necessary, which are provided free of charge by the laboratories on request. Do not refrigerate or freeze the samples; storage and transport of samples is at room temperature. If proper incubation is possible on site, this should be attempted; information is available from the laboratory. Contact addresses: Dr. A.-M. Fahr; Dr. A. Turnwald-Maschler; Dr. M. Holfelder: Tel.: 06221-3432-125/262/234

Literature
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Detjen A et al (2006). Immunological diagnostics of tuberculosis interferon γ tests. monthly journal Kinderheilkd 154: 152-159
Ewer K et al(2003) Comparison of T-cell-based assay with tuberculin skin test for diagnosis of Mycobacterium tuberculosis infection in a school tuberculosis outbreak. Lancet 361:1168-1173
Hauer B et al.(2006) Interferon-γ tests in tuberculosis diagnostics - Current status. Pneumology 60: 29-44.
Lange C et al.(2006). Current status of tuberculosis diagnostics. Dtsch Med weekly 131: 341-347