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Interferon-gamma release assays (IGRAs) are diagnostic tools for latent tuberculosis infection (LTBI). They are surrogate markers of Mycobacterium tuberculosis infection and indicate a cellular immune response to M. tuberculosis. IGRAs cannot distinguish between latent infection and active tuberculosis (TB) disease, and should not be used as a sole method for diagnosis of active TB, which is a microbiological diagnosis. A positive IGRA result may not necessarily indicate TB infection, but can also be caused by infection with non-tuberculous mycobacteria. A negative IGRA does not rule out active TB disease; a number of studies have shown that up to a quarter of patients with active TB have negative IGRA results.
Because IGRAs are not affected by Bacille Calmette-Guérin (BCG) vaccination status, IGRAs are useful for evaluation of LTBI in BCG-vaccinated individuals, particularly in settings where BCG vaccination is administered after infancy or multiple (booster) BCG vaccinations are given. In contrast, the specificity of tuberculin skin test (TST) varies depending on timing of BCG and whether repeated (booster) vaccinations are given.
QuantiFERON, also known as QFT, is the registered trademark of the test for tuberculosis infection or latent tuberculosis . It is manufactured by QIAGEN . QFT is an interferon-γ release assay (IGRA) used in tuberculosis diagnosis .
The QFT-GIT assay is an ELISA-based, whole-blood test that uses peptides from three TB antigens (ESAT-6, CFP-10, and TB7.7) in an in-tube format. The result is reported as quantification of IFN-gamma in international units (IU) per mL. An individual is considered positive for M. tuberculosis infection if the IFN-gamma response to TB antigens is above the test cut-off (after subtracting the background IFN-gamma response in the negative control).
- 1 QuantiFERON-TB (QFT)
- 2 QuantiFERON-TB Gold
- 3 QuantiFERON-TB Gold In-Tube
- 4 Availability
- 5 References
QuantiFERON-TB (QFT)[ edit ]
QuantiFERON-TB Gold In-Tube (QFT-GIT) , the third generation test, has replaced QuantiFERON-TB (QFT) and QuantiFERON-Gold, which are no longer marketed.
According to the U.S. Centers for Disease Control ,  in 2001, the QuantiFERON-TB test (QFT) was approved by the Food and Drug Administration (FDA) as an aid for detecting latent Mycobacterium tuberculosis infection. This test is an in vitro diagnostic aid that measures a component of cell-mediated immune reactivity to M. tuberculosis. The test is based on the quantification of interferon-gamma (IFN-γ) released from sensitized lymphocytes in whole blood incubated overnight with purified protein derivative (PPD) from M. tuberculosis and control antigens.
Tuberculin skin testing (TST) has been used for years as an aid in diagnosing latent tuberculosis infection (LTBI) and includes measurement of the delayed type hypersensitivity response 48–72 hours after intradermal injection of PPD. TST and QFT do not measure the same components of the immunologic response and are not interchangeable. Assessment of the accuracy of these tests is limited by lack of a standard for confirming LTBI.
As a diagnostic test, QFT:
- requires phlebotomy
- can be accomplished after a single patient visit
- assesses responses to multiple antigens simultaneously
- does not boost anamnestic immune responses (see Latent tuberculosis#Boosting ).
Compared with TST, QFT results are less subject to reader bias and error. In a CDC-sponsored multicenter trial, QFT and TST results were moderately concordant (overall kappa value = 0.60). The level of concordance was adversely affected by prior bacille Calmette-Guérin (BCG) vaccination , immune reactivity to nontuberculous mycobacteria (NTM), and a prior positive TST.  In addition to the multicenter study, two other published studies have demonstrated moderate concordance between TST and QFT.   However, one of the five sites involved in the CDC study reported less agreement.  Although there have been studies confirming the increased future risk of active TB in individuals with positive TST, the same was not true for those with a positive IGRA result. A recently published study  demonstrated that a positive IGRA result is predictive of future active TB risk. Moreover, IGRA was at least as sensitive and was more specific compared to traditional TST. In this study of immunocompetent recently exposed close contacts of active TB cases, the progression rate to active disease among untreated QFT positive individuals was significantly greater than for untreated TST positives (14.6% versus 2.3%). Although the numbers were small, all of the close contacts who went on to develop active TB were QFT positive, but only 83% were TST positive.
As noted above, prior BCG vaccination can produce false positive TST results. In a study of military personnel returning from missions, about one-half of the positive TSTs were falsely positive.  In a more recent study of military returning from missions, Franken et al.  reported evidence suggesting false positive TST results are common and that QFT testing could guide more targeted treatment and alleviate unnecessary anti-tuberculous treatment.
The FDA’s cutpoint for a positive result was established at >0.34 International Units/millilitre (IU/ml), though this has proven functionally problematic in low prevalence areas, such as among US and Canadian healthcare workers. In areas of low risk and low prevalence, the positive predictive value of any test is diminished. In the case of serially screened North American healthcare workers, QFT results just above this cutpoint produce false-positive test results that upon repeat testing revert to negative,  where tuberculosis screening is often mandated on an annual basis (MMWR June 2010, https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5905a1.htm?s_cid=rr5905a1_e Research at Stanford University and the Veterans Administration has reported the use of a retesting (or borderline) zone below 1.1 IU/ml mitigates 76% of the false-positives, or reversions.,  
Limitations of QFT include the need to draw blood and process it within 16 hours after collection and limited laboratory and clinical experience with the assay. There is need for further study of the utility of QFT in predicting the progression to active tuberculosis, particularly in children and immunocompromised hosts.Thanassi, 2012 #6
To its disadvantage, QFT can yield false positive results with Mycobacterium szulgai , Mycobacterium kansasii , and Mycobacterium marinum . 
QuantiFERON-TB Gold[ edit ]
The QuantiFERON-TB Gold test (QFT-G) is a whole-blood test for use as an aid in diagnosing Mycobacterium tuberculosis infection, including latent tuberculosis infection (LTBI) and tuberculosis (TB) disease.  This test was approved by the U.S. Food and Drug Administration (FDA) in 2005.
Blood samples are mixed with antigens (substances that can produce an immune response) and controls. For QFT-G, the antigens include mixtures of synthetic peptides representing two M. tuberculosis proteins, ESAT-6 and CFP-10 . 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 . The QFT-G results are based on the amount of IFN-gamma that is released in response to the antigens.
Clinical evaluation and additional tests (such as a chest radiograph , sputum smear, and culture) are needed to differentiate between a diagnosis of latent TB or active TB.
Advantages of the test are:
- 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.
Disadvantages and limitations of the test are:
- Blood samples must be processed within 16 hours after collection while white blood cells are still viable.
- There is 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.
QuantiFERON-TB Gold In-Tube[ edit ]
On 10/10/2007 the US FDA  gave approval for the Quantiferon TB Gold In Tube to be marketed in the US
The FDA states:
Approval for a modification of the quantiferon-tb gold to an in-tube collection system that consists of three blood collection tubes, nil, tb antigen, and mitogen. The device, as modified, will be marketed under the trade name quantiferon-tb gold in-tube and is indicated for use as an in vitro diagnostic test using a peptide cocktail simulating esat-6, cfp-10 and tb 7.7(p4) proteins to stimulate cells in heparinized whole blood drawn directly into specialized blood collection tubes. Detection of interferon-y by enzyme-linked immunosorbent assay (elisa) is used to identify in vitro responses to these peptide antigens that are associated with mycobacterium tuberculosis infection.
According to the FDA approved package insert  Quantiferon TB Gold In Tube has a consistent specificity of >99% in low risk individuals and a sensitivity as high as 92% in individuals with active disease, depending on setting and extent of disease. The specificity in two studies of a few hundred people is 96-98% in a health immunised population.
The package insert also advises that the kit provides three collection tubes which have had antigens dried onto their walls and that these tubes must be transferred to an incubator within 16 hours of blood collection.
On 25 June 2010, the US Centers for Disease Control and Prevention (CDC) updated the tuberculosis (TB) testing guidelines (MMWR June 2010, https://www.cdc.gov/mmwr/pdf/rr/rr5905.pdf )[ permanent dead link ] providing guidance to US public health officials, clinicians, and laboratory workers regarding screening for and diagnosis of TB infection. The updated guidelines provide new direction for TB control in the US.
Previously, QuantiFERON®-TB Gold was able to be used in any situation in which the Tuberculin Skin Test (TST) was used, without preference. The 2010 guidelines establish a new benchmark because they recommend IGRAs as the preferred TB testing method in many patients, including those who are BCG vaccinated or are unlikely to return for TST reading.
Medical facilities in the US using QFT can be found at http://www.quantiferon.com/irm/content/contact-us1.aspx?RID=342 .
Availability[ edit ]
In the United States, the test is widely available from state public health laboratories, hospitals, and commercial laboratories .
In January 2008 the CDC advised – via their TB Notes Newsletter  – TB controllers and others of a link  to a list of laboratories in the US and Canada offering to perform the Quantiferon Gold test.
The California Tuberculosis Controllers Association have also provided a list of public health laboratories  in California that are testing with Quantiferon.
References[ edit ]
- ^ Gerald H. Mazurek; Margarita E. Villarino. “Guidelines for Using the QuantiFERON-TB Test for Diagnosing Latent Mycobacterium tuberculosis Infection” . Retrieved 2007-06-01.
- ^ Mazurek, GH; LoBue, PA; Daley, CL; Bernardo, J; Lardizabal, AA; Bishai, WR; Iademarco, MF; Rothel, JS (Oct 10, 2001). “Comparison of a whole-blood interferon gamma assay with tuberculin skin testing for detecting latent Mycobacterium tuberculosis infection”. Journal of the American Medical Association. 286 (14): 1740–7. doi : 10.1001/jama.286.14.1740 . PMID 11594899 .
- ^ Pottumarthy, S; Morris, AJ; Harrison, AC; Wells, VC (Oct 1999). “Evaluation of the tuberculin gamma interferon assay: potential to replace the Mantoux skin test” . Journal of Clinical Microbiology. 37 (10): 3229–32. PMC 85534 . PMID 10488182 .
- ^ Streeton, JA; Desem, N; Jones, SL (Jun 1998). “Sensitivity and specificity of a gamma interferon blood test for tuberculosis infection”. The International Journal of Tuberculosis and Lung Disease. 2 (6): 443–50. PMID 9626600 .
- ^ Bellete, B; Coberly, J; Barnes, GL; Ko, C; Chaisson, RE; Comstock, GW; Bishai, WR (Jun 1, 2002). “Evaluation of a whole-blood interferon-gamma release assay for the detection of Mycobacterium tuberculosis infection in 2 study populations”. Clinical Infectious Diseases. 34 (11): 1449–56. doi : 10.1086/340397 . PMID 12015690 .
- ^ Diel, R; Loddenkemper, R; Meywald-Walter, K; Niemann, S; Nienhaus, A (May 15, 2008). “Predictive value of a whole blood IFN-gamma assay for the development of active tuberculosis disease after recent infection with Mycobacterium tuberculosis”. American Journal of Respiratory and Critical Care Medicine. 177 (10): 1164–70. doi : 10.1164/rccm.200711-1613OC . PMID 18276940 .
- ^ Bruins, J; Gribnau, JH; Bwire, R (Dec 1995). “Investigation into typical and atypical tuberculin sensitivity in the Royal Netherlands Army, resulting in a more rational indication for isoniazid prophylaxis”. Tubercle and Lung Disease. 76 (6): 540–4. doi : 10.1016/0962-8479(95)90531-6 . PMID 8593376 .
- ^ Franken, WP; Timmermans, JF; Prins, C; Slootman, EJ; Dreverman, J; Bruins, H; van Dissel, JT; Arend, SM (Apr 2007). “Comparison of Mantoux and QuantiFERON TB Gold tests for diagnosis of latent tuberculosis infection in Army personnel” . Clinical and Vaccine Immunology. 14 (4): 477–80. doi : 10.1128/CVI.00463-06 . PMC 1865601 . PMID 17301213 .
- ^ Zwerling, A; Benedetti, A; Cojocariu, M; McIntosh, F; Pietrangelo, F; Behr, MA; Schwartzman, K; Menzies, D; Pai, M (2013). “Repeat IGRA testing in Canadian health workers: conversions or unexplained variability?” . PLoS ONE. 8 (1): e54748. doi : 10.1371/journal.pone.0054748 . PMC 3561382 . PMID 23382955 .
- ^ Thanassi, Wendy; Noda, Art; Hernandez, Beatriz; Newell, Jeffery; Terpeluk, Paul; Marder, David; Yesavage, Jerome A. (2012). “Delineating a Retesting Zone Using Receiver Operating Characteristic Analysis on Serial QuantiFERON Tuberculosis Test Results in US Healthcare Workers”. Pulmonary Medicine. 2012: 1–7. doi : 10.1155/2012/291294 .
- ^ Behrman, A; Buchta, WG; Budnick, LD; Hodgson, MJ; Raymond, LW; Russi, M; Spillmann, SJ; Swift, MD (Aug 2013). “Protecting Health Care Workers From Tuberculosis, 2013: ACOEM Medical Center Occupational Health Section Task Force on Tuberculosis and Health Care Workers”. Journal of Occupational and Environmental Medicine. 55 (8): 985–8. doi : 10.1097/JOM.0b013e3182a0d7cd . PMID 23887706 .
- ^ “Clinicians guide to QuantiFERON-TB” (PDF). Cellestis Inc. November 2001. Retrieved 2009-05-15.
- ^ Division of Tuberculosis Elimination (2004-04-18). “QuantiFERON-TB Gold Test” . Retrieved 2007-06-01.
- ^ “Center for Devices and Radiological Health” . FDA. 2007-10-10. Retrieved 2009-01-03.
- ^ “Quantiferon-TB Gold In-Tube Package Insert” . Cellestis. 2007-10-10. Archived from the original on 2008-07-19. Retrieved 2009-01-03.
- ^ “TB Notes Newsletter” . CDC. 2008-01-02. Retrieved 2009-01-03.
- ^ “Laboratories Offering QFT Testing” . Cellestis. Retrieved 2009-01-03.
- ^ “(CALIFORNIA) COUNTY PUBLIC HEALTH LABS PERFORMING QUANTIFERON” (PDF). CTCA. 2007-03-01. Archived from the original (PDF) on 2007-06-27. Retrieved 2009-01-03.
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QuantiFERON®-TB Gold blood test
Tuberculosis (TB) is a contagious disease caused by the bacterium called Mycobacterium tuberculosis, which usually infects the lungs, but also can spread to any part of the body including the kidney, spine, and brain. TB, if not treated properly, can even be fatal.1 The TB bacillus is typically spread through the air via respiratory droplets when a person with respiratory TB disease sneezes or coughs onto other individuals in close proximity.1,2
What is QuantiFERON®-TB Gold blood test?
An alternative to the tuberculin skin test (TST)
The QuantiFERON®-TB Gold blood test (QFT-G) is a blood test for use as an aid in diagnosing Mycobacterium tuberculosis infection (both latent tuberculosis infection and active tuberculosis disease).3 The test is approved by the U.S. Food and Drug Administration (FDA) for use with adult patients.
CDC Statement: 4
"The greater specificity of the Quantiferon test and the requirement for only one visit are compelling advantages."
CDC Specific Recommendations: 8(June 2010)
- Interferon-Gamma Release Assays (IGRAs) may be used in place of (but not in addition to) a TST in all situations in which the CDC recommends TST as an aid in diagnosing M. tuberculosis infection.
- IGRA is preferred for testing persons who have received BCG (as a vaccine or for cancer therapy).
- IGRA is preferred for testing persons who have received BCG (as a vaccine or for cancer therapy).
- An IGRA may be used in place of TST (without preference) to test recent contacts of persons with infectious tuberculosis with special considerations for follow-up testing. In contact investigations, negative results obtained prior to 8 weeks typically should be confirmed by repeat testing 8-10 weeks after the end of exposure.
How does QuantiFERON®-TB Gold blood test work?
The QFT-G is an indirect test for M. tuberculosis infection that is based on measurement of a cell-mediated immune response. A cocktail of 3 mycobacterial proteins (ESAT-6, CFP-10, and TB 7.7) stimulate the patient’s T-cells in vitro to release interferon-gamma, which is then measured using ELISA technology. The test detects infections produced by the M. tuberculosis complex (including M. tuberculosis, M. bovis, and M. africanum infections). BCG strains and the majority of other non-tuberculosis mycobacteria do not harbor ESAT-6, CFP-10, and TB 7.7 proteins; thus, patients either vaccinated with BCG or infected with most environmental mycobacteria should test negative. Results should always be interpreted in conjunction with other clinical and laboratory findings.
What are the advantages of QuantiFERON®-TB Gold blood test over tuberculin skin test (TST)? 3
- Improved specificity6
- Results are not subject to reader bias
- Results are not affected by the booster phenomenon (i.e., increased sensitivity on subsequent test, leading to false-positive results)
- Accuracy is not affected by prior BCG (bacille Calmette-Guérin) vaccination
- Requires only 1 patient visit (2-4 required for TST)
- Cost savings from reduced staff time and avoidance of unnecessary follow-up testing and treatment5
Who developed QuantiFERON®-TB Gold blood test?
Cellestis Limited, a listed Australian biotechnology company founded in 2000 in Melbourne, Australia, develops and manufactures the QuantiFERON®-TB Gold blood test, a breakthrough blood test for the detection and control of tuberculosis. The QuantiFERON®-TB Gold technology is a patented method for detecting cell mediated immune (CMI) responses of T-cell lymphocytes using whole blood samples. QuantiFERON®-TB Gold test is available nationally through Quest Diagnostics.
The performance of the USA format of the QuantiFERON®-TB Gold blod test has not been extensively evaluated with specimens from the following groups of individuals:7
- Individuals who have impaired or altered immune function such as those who have HIV infection or AIDS, those who have transplantation managed with immunosuppressive treatment or others who receive immunosuppressive drugs (e.g. corticosteroids, methotrexate, azathioprine, cancer chemotherapy), and those who have other clinical conditions: diabetes, silicosis, chronic renal failure, hematological disorders (e.g., leukemia and lymphomas), and other specific malignancies (e.g., carcinoma of the head or neck and lung).
- Individuals younger than age 17 years.
- Pregnant women.
Contact a Quest Diagnostics Sales Representative, learn more about our testing services, and become a client
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1 CDC TB Basic Facts http://www.cdc.gov/tb/topic/basics/default.htm. Accessed 2/24/10.
2 World Health Organization. Tuberculosis Infection and Transmission http://www.who.int/mediacentre/factsheets/fs104/en/index.html. Accessed 3/1/10.
3 CDC Fact Sheet: QuantiFERON®-TB Gold Test. National Center for HIV/AIDS, Viral Hepatitis, and TB Prevention; Division of Tuberculosis Elimination (DTBE) Web site http://www.cdc.gov/tb/pubs/tbfactsheets/QFT.htm. Last reviewed April 18, 2007. Accessed October 5, 2007.
4 National Tuberculosis Controllers Association; Centers for Disease Control and Prevention (CDC). MMWR Recomm Rep. 2005;54(RR-15):1-47.
5 Lambert et al. Infection Control and Hospital Epidemiology. 2003; 24:814-820.
6 Diel et al. Evidence-based comparison of commercial interferon-gamma release assays for detecting active TB: a metaanalysis. Chest. 2010 Apr;137(4):952-68. Epub 2009 Dec 18.
7 FDA Device Approvals and Clearances Page: http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ DeviceApprovalsandClearances/Recently-ApprovedDevices/ucm084025.htm.
8 National Tuberculosis Controllers Association; Centers for Disease Control and Prevention (CDC). MMWR Recomm Rep. 2010;59 (RR-5): June 25, 2010.