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definition - QuantiFERON

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QuantiFERON

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QuantiFERON is the registered trademark of two tests for tuberculosis or latent tuberculosis, manufactured by Cellestis Limited, Carnegie, Victoria, Australia. These are interferon-γ release assays used in tuberculosis diagnosis.

Contents

QuantiFERON-TB

QuantiFERON-TB has been replaced by QuantiFERON-TB Gold and is no longer marketed.

According to the U.S. Centers for Disease Control,[1]

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 (1). 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 1) requires phlebotomy, 2) can be accomplished after a single patient visit, 3) assesses responses to multiple antigens simultaneously, and 4) does not boost anamnestic immune responses. 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 (2). In addition to the multicenter study, two other published studies have demonstrated moderate concordance between TST and QFT (3,4). However, one of the five sites involved in the CDC study reported less agreement (5).

Limitations of QFT include the need to draw blood and process it within 12 hours after collection and limited laboratory and clinical experience with the assay. The utility of QFT in predicting the progression to active tuberculosis has not been evaluated.

QuantiFERON-TB Gold

According to the U.S. Centers for Disease Control,[2]

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 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.
  • False positive results can occur with Mycobacterium szulgai, Mycobacterium kansasii, and Mycobacterium marinum.[3]

QuantiFERON-TB Gold In-Tube

On 10/10/2007 the US FDA [4] gave approval for the Quantiferon TB Gold In Tube to be marketed in the US

The FDA state:
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[5] 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.

Availability

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[6] - TB controllers and others of a link[7] 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 [8] in California that are testing with Quantiferon

References

 

All translations of QuantiFERON


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