The Most Accurate Test for TB Infection QuantiFERON®-TB Gold
www.QuantiFERON.com
The key to the eradication of TB is prevention Tuberculosis (TB) continues to infect people in both developed and developing countries. At least two billion people are thought to be infected with Mycobacterium tuberculosis, a bacterium that is the primary cause of TB. Detection and treatment of active and latent TB infection (LTBI) are part of effective disease prevention (Figure 1). Infections per million
2000 1770
1600
Active TB case detection and treatment 1200 800 400
Mass LTBI detection and treatment Active and latent TB detection and treatment
0 2010
2020
2030
2015
2040
2050
Years
Figure 1. Benefits of fighting active and latent TB (1).
The World Health Organization (WHO) acknowledges that to fight TB effectively, the accurate identification and treatment of latent TB infections, as well as active TB disease are vital (2).
Those at greatest risk should be prioritized for screening (3–9):
Healthcare workers (HCWs) Military personnel Elderly people Students Immigrants Close contacts of persons known or suspected to have active TB People who are residents in long-term care facilities People with weakened immune systems Prison inmates and persons living in other congregate settings Why not choose the most clinically proven, modern testing solution? QuantiFERON-TB Gold (QFT®) is a highly specific, controlled blood test to aid in the diagnosis of infection with M. tuberculosis. Known as an interferon-gamma release assay (IGRA), QFT provides the value of robust technology. QFT is the ideal solution for the accurate identification of TB infection that is needed for effective disease prevention.
2
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The Most Accurate Test for TB Infection 09/2014
The modern replacement for the tuberculin skin test Unlike the tuberculin skin test (TST), QFT is a controlled laboratory test that requires only one patient visit and is unaffected by previous vaccination with Bacille-Calmette Guerin (BCG; see references 4, 10, and 11; and Table 1). QFT is a highly accurate, cost-effective testing solution. QFT has unique blood collection tubes (Figure 2), enabling immediate exposure of blood lymphocytes to highly specific TB antigens and test controls coated on the inner surface of the tubes. The Nil tube (negative control) adjusts for background interferon gamma (IFNγ). The Mitogen tube serves as a positive control and can be useful for indicating correct sample handling and incubation, as well as a patient’s immune status. The TB Antigen tube contains highly-specific TB antigens, ESAT6/CFP-10/TB-7.7(p4).
Table 1. A modern test for TB infection — QuantiFERON-TB Gold QFT (4, 10)
TST (10, 13)
Process
Requires only one patient visit, controlled laboratory test
In vivo Purified Protein Derivative (PPD) reaction requires two patient visits, test without controls
Performance specifications (10)
Sensitivity — 84%
Sensitivity — 70%
Specificity — 99%
Specificity — highly variable (population dependent: 59% in BCG vaccinated people)
Sample input
Incubated whole blood
Injected PPD into the skin
Performance in immunosuppressed populations (14, 15)
Proven performance in patients who are taking immune suppression therapies (methotrexate, corticosteroids, TNF-α inhibitors)
Limited sensitivity, especially in immunosuppressed patients
Measurement
Detection of IFN-γ by optical density measurement
Measures skin induration, highly subjective, high inter/intra-observer variability
Cross reactivity with BCG
Unaffected by BCG vaccination or most other mycobacteria
Results affected by BCG vaccination and other mycobacteria
Objective results
Objective, reproducible results, uses QFT analysis software
Subjective result — visual interpretation (induration in millimeters) after 48–72 hours
Cost effectiveness (16, 17)
Consistently shown to be more cost effective than TST in multiple screening situations (healthcare workers, immigration, contact tracing)
Cheap reagents but high program costs (due to second visit and false positives)
Figure 2. QuantiFERON-TB Gold blood collection tubes. (L to R) Nil tube (negative control), TB Antigen tube, and Mitogen tube (positive control). The TB Antigen tube assesses IFN-γ response to highly specific TB antigens. The Mitogen tube can be useful to indicate patient’s immune status and correct blood handling and incubation. The Nil tube adjusts for background IFN-γ.
The US Centers for Disease Control (CDC) Guidelines recommend the use of IGRAs in all situations in which the TST was historically used, with IGRAs being the preferred test for persons who have been BCG vaccinated or are unlikely to return for TST reading (3).
QFT has well-established clinical utility and is the most clinically tested and proven IGRA (12). Rely on the only LTBI test that offers:
Objective and reproducible results Convenient ELISA technology with objective analysis software Greater than 900 clinical and scientific studies
The Most Accurate Test for TB Infection 09/2014
www.QuantiFERON.com
3
QFT provides a new paradigm in diagnosing TB infection When compared with other IGRA products, which require subjective counting of spots, QuantiFERON-TB Gold provides quantitative detection with a user-friendly workflow (Tables 2 and 3). Table 2. QuantiFERON-TB Gold vs. other IGRAs on the market QFT (4, 10)
ELISpot without Xtend® (10, 18)
ELISpot with Xtend (18)
Sensitivity — 84%
Sensitivity — 89%
Unknown
Specificity — 99%
Specificity — 86%
Sample input
Incubated whole blood
Separated peripheral blood mononuclear cells
Separated peripheral blood mononuclear cells, incubated with T-cell Xtend reagent
Blood draw dependent on age or immune status?
No
Yes. 2 ml for
