QuantiFERON®-TB Gold Assessment of Tuberculosis Exposure
(June 2007)
(Download 
QuantiFERON.pdf)
Background
Cell-mediated immunity controls infections caused by intracellular pathogens such as Mycobacterium tuberculosis (M.tb), and involves helper (CD4+) T cell-driven granuloma formation. In the absence of prior treatment with antituberculous therapy, the demonstration of immunological memory for M.tb implies the presence of ongoing TB infection, which may be either silent and asymptomatic (“latent” TB infection, LTBI), or active and symptomatic, often involving the lungs and presenting with fever and productive cough.
“QuantiFERON®-TB Gold test”
The traditional method for demonstrating tuberculosis sensitization, the tuberculin skin test or “Mantoux” test, is increasingly being replaced by the TB Gold in-vitro blood test method. In this test, patient whole blood samples are mixed with two M. tuberculosis proteins, ESAT-6 and CFP-10, as well as controls. If the patient has been exposed to M. tuberculosis, T helper lymphocytes will release interferon-gamma (IFN-gamma) in response to contact with the TB antigens, which is then measured using an ELISA.
Advantages and Disadvantages of TB Gold vs Mantoux
QFT-G can be used in all circumstances in which the Mantoux test is currently used, including contact investigations, and TB screening of recent immigrants & health care workers. However, efficacy data for the use of QFT-G are limited in some situations (see below).
Advantages over Mantoux:
- Is not affected by prior BCG (Bacille Calmette-Guerin) vaccination.
- Requires a single patient visit to draw a blood sample
- Does not boost responses measured by subsequent tests
- Is not subject to reader bias
Disadvantages & Limitations:
- Blood samples must be processed within 16 hours of collection
- Data limited on use of TB Gold in children younger than 17 years of age, persons recently exposed to M. tuberculosis, and immunocompromised persons (e.g., HIV infection or current treatment with immunosuppressive drugs)
- Cross-reactivity with M.szulgai, M.kansasii and M.marinum infections
- For recent contacts of TB exposure, an 8 – 10 week false-negative “window” may exist
Indications
- Screening for Mycobacterial infection, latent or otherwise, is recommended prior to commencing potent immunomodifying drugs e.g. Infliximab , adalumimab and Etanercept
- The test is Medicare-rebatable in immuno-suppressed or immuno-compromised individuals, including those with HIV infection or autoimmune conditions managed with immune suppressants (item number 69471)
- For those patients who do not meet these guidelines, a charge of $60 will be levied.
Specimen Collection
- Special collection tubes are required, for further information on collection of specimens please contact the laboratory on 02 49214018.
- Due to the incubation step required, samples should not be collected on Fridays or weekends.
Please note this test is primarily intended to detect latent infection with M.TB, and not for the diagnosis and management of active tuberculosis. Should active TB be suspected, culture (and/or PCR testing) of appropriate clinical specimens is necessary.
Immunology Contacts
Dr Glenn Reeves / Dr Theo de Malmanche (Clinical Staff Specialists) – 49214018
Prof Robert Clancy (Director/Clinical staff specialist) – 49214018
Immunology Laboratory - 49214018