QuantiFERON®–TB Gold Plus (QFT-Plus) is the updated version of the QuantiFERON®–TB Gold (QTF) test.

Like its predecessor, QFT-Plus is a simple blood test that aids in the diagnosis of exposure to Mycobacterium tuberculosis, the bacteria which causes tuberculosis (TB). QFT-Plus is an interferon gamma release assay, commonly known as an IGRA, and is a modern alternative to the tuberculin skin test (TST). Unlike the TST, QFT-Plus is a controlled laboratory test that requires only one patient visit and works on patients who have previously been vaccinated against TB with the Bacille Calmette-Guerin (BCG) vaccination.

Compared to QFT, the QFT-Plus test is optimized with innovative TB-specific antigens that elicit both CD4 and CD8 T cell responses – giving a more comprehensive assessment of the patient’s immune response to TB infection.

Along with accurately detecting active TB, QFT-Plus also diagnoses Latent TB Infection (LTBI) which is an asymptomatic infection, and is believed to affect over one-quarter of the global population. LTBI is a state of persistent immune response with evidence of clinically active TB. Approximately 5-15% of infected individuals will progress to active TBI if not diagnosed and treated. This progression is called the reactivation of LTBI.

QFT-Plus measures the amount of interferon gamma that is released when infected white blood cells in a blood sample come into contact with specific antigens of M. tuberculosis. The test is simple, fast and considered the most clinically tested and proven. The use of whole blood in QFT-Plus makes T cell incubation simple and fast, and reduces turn-around time (TAT). It is simple as there is no lymphocyte isolation, washing, counting, diluting, or culturing.

The QFT-Plus Test can be used be used for individuals who:

• Have had contact with persons diagnosed with active pulmonary TB,
• Are at increased risk of progression to active TB disease due to impaired immunity,
• Have radiographic evidence of old, healed TB without history of treatment and
• Have an increased risk for LTBI due to injection-drug use.

Additionally, the following individuals should be screened for tuberculosis:

• Foreign-born persons and visitors from TB-endemic countries, especially immigrants who have arrived in the last two years
• Residents and employees of prisons and jails
• Individuals eligible for LTBI surveillance programs such as health-care workers, aid workers and military personnel
• Screening for LTBI is viewed as precautionary in management of patients with the following inflammatory diseases: rheumatoid arthritis, ulcerative colitis, psoriasis and psoriatic arthritis, ankylosing spondylitis, and Crohn’s disease.

The QFT-Plus test works on patients who have previously been vaccinated against TB with the Bacille Calmette-Guerin (BCG) vaccination. QFT-Plus requires only one patient visit to a LifeLabs location, has a high sensitivity (>94%) and high specificity (>97%) which reduces unnecessary evaluations (labs, X-rays).

QFT is approved by both FDA and Health Canada as a diagnostic test to detect Mycobacterium tuberculosis infection.

The whole blood sample is collected in 4 specialized tubes that enable immediate exposure of the white blood cells to highly specific TB antigens (ESAT-6, CFP-10 and proprietary CD8 antigens). Only 1 ml of whole blood is required per tube.

The QFT-Plus results are reported qualitatively as negative or positive for the bacteria, as well as quantitatively with a numerical value (reported in IU/mL). The numerical value indicates the amount of interferon gamma that is released when infected blood cells are exposed to specific antigens of M.tuberculosis.

In healthy persons who have a low likelihood both of M. tuberculosis infection and of progression to active tuberculosis if infected, a single positive QFT-Plus result should not be taken as reliable evidence of M. tuberculosis infection. Repeat testing, with either the initial test or a different test, may be considered on a case-by-case basis.

In Ontario, the test may be ordered on the standard OHIP requisition. In BC, a specific QFT-Plus requisition is required to be filled and signed by the healthcare provider. Your patient must bring the requisition form signed by you to one of our locations.

Please note that this test is offered in select LifeLabs locations only. To order this test for your patient, please advise them of the price (C$95.00) and have them book an appointment at one of our select locations, listed below.  

The QFT test is available in select LifeLabs locations in Ontario & BC. Please refer to the link for more details.

1. Qiagen, QuantiFERON®–TB Gold Plus product information
2. Pai et. al. Canadian Tuberculosis Standards 7th Edition: 2014 – Diagnosis of latent Tuberculosis infection
3. Centers for Disease Control and Prevention, Guidelines for Using the QuantiFERON®-TB Test for Diagnosing Latent Mycobacterium tuberculosis Infection, 2012
4. CDC. Updated guidelines for using gamma release assays to detect m. tuberculosis infection. MMWR. 2010;59(RR05):1-25
5. City of Toronto, Tuberculosis Information for Healthcare Providers: Management of Latent Tuberculosis Infection and Active Disease – Information for Health Professionals
6. Latent tuberculosis infection: An overview – CCDR: Volume 43-3/4, March 2, 2017: Tuberculosis (TB)
7. World Health Organization’s Fact Sheet on Tuberculosis