What is QuantiFeron-TB Gold?
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We all know the simple, classical, widely used, method of diagnostic/screening of tuberculosis, the Mantoux test (also known as the Mantoux screening test, Tuberculin Sensitivity Test, Pirquet test, or PPD test for Purified Protein Derivative),has a low specificity-may give a false positive or negative. Therefore a new method of diagnostics was invented and is being perfected to replace mantoux test
QuantiFERON®-TB Gold is an in vitro laboratory diagnostic test using a whole blood specimen. It is an indirect test for M. tuberculosis complex (i.e., M. tuberculosis, 
M. bovis, M. africanum, M. microti, M.canetti) infection, whether tuberculosis disease (TB) or latent tuberculosis infection (LTBI).
This diagnostic test uses peptide cocktails simulating ESAT-6 and CFP-10 proteins to stimulate cells in heparinized whole blood. These proteins are absent from all BCG strains and from most non-tuberculosis mycobacteria with the exception of M. kansasii, M. szulgai and M. marinum. Individuals infected with M. tuberculosis-complex organisms usually have lymphocytes in their blood that recognize these and other mycobacterial antigens. This recognition process involves the generation and secretion of interferon-γ (IFN-γ). The detection and subsequent quantification of IFN-γ forms the basis of the QuantiFERON®-TB Gold test.
At least 4 mL of heparinized whole blood collected by venipuncture is needed for testing. An evacuated tube (5, 9, or 10 mL) with heparin should be completely filled. Anti-coagulants other than heparin are not suitable. Blood tubes should be held and transported at room temperature (22° ± 5°C) and must be transported to laboratories to allow initiation of testing within 12 hr. After incubation of the blood with antigens for 16 to 24 hours, the amount of interferon-gamma (IFN-gamma) is measured. If the patient is infected with M. tuberculosis, their white blood cells will release IFN-gamma in response to contact with the TB antigens.
What are the advantages?
- Requires a single patient visit to draw a blood sample.
- Results can be available within 24 hours.
- Does not boost responses measured by subsequent tests, which can happen with tuberculin skin tests (TST).
- Is not subject to reader bias that can occur with TST.
- Is not affected by prior BCG (bacille Calmette-Guérin) vaccination.
What are the disadvantages and limitations?
- Blood samples must be processed within 12 hours after collection while white blood cells are still viable.
- There are limited data on the use of QFT-G in children younger than 17 years of age, among persons recently exposed to M. tuberculosis, and in immunocompromised persons (e.g., impaired immune function caused by HIV infection or acquired immunodeficiency syndrome [AIDS], current treatment with immunosuppressive drugs, selected hematological disorders, specific malignancies, diabetes, silicosis, and chronic renal failure).
- Errors in collecting or transporting blood specimens or in running and interpreting the assay can decrease the accuracy of QFT-G.
- Limited data on the use of QFT-G to determine who is at risk for developing TB disease.
A diagnosis of LTBI requires that TB disease be excluded by medical evaluation, which should include checking for signs and symptoms suggestive of TB disease, a chest radiograph, and, when indicated, examination of sputum or other clinical samples for the presence of M. tuberculosis.