QuantiFERON
Encyclopedia
QuantiFERON, also known as QFT, is the registered trademark of the test for tuberculosis infection or latent tuberculosis
. QFT is an interferon-γ release assay (IGRA) used in tuberculosis diagnosis
.
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 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 (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.
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. There is need for further study of the utility of QFT in predicting the progression to active tuberculosis, particularly in children and immunocompromised hosts.
According to the U.S. Centers for Disease Control, 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 peptide
s 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 cell
s 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:
Disadvantages and limitations of the test are:
The FDA state:
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, http://www.cdc.gov/mmwr/pdf/rr/rr5905.pdf) 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.
• are unlikely to return for TST reading
nn
Medical facilities in the US using QFT can be found at http://www.cellestis.com/IRM/content/usa/contact_quantiferon.html. {Clicking on their column heading "State" twice will sort listings alphabetically by state. Likely more useful than their current default listing by alphabetical order of "Testing Facility" names}
.
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
Latent tuberculosis
Also called latent tuberculosis infection, latent TB or LTBI.Latent tuberculosis is where a patient is infected with Mycobacterium tuberculosis, but does not have active tuberculosis disease. Patients with latent tuberculosis are not infectious, and it is not possible to get TB from someone with...
. QFT is an interferon-γ release assay (IGRA) used in tuberculosis diagnosis
Tuberculosis diagnosis
Tuberculosis is diagnosed by finding Mycobacterium tuberculosis bacteria in a clinical specimen taken from the patient. While other investigations may strongly suggest tuberculosis as the diagnosis, they cannot confirm it.-Diagnosis:...
.
QuantiFERON-TB (QFT)
QuantiFERON-TB Gold QFT-G and QuantiFERON-TB Gold In-Tube QFT-GIT, have replaced QuantiFERON-TB (QFT), which is 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
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
(FDA) as an aid for detecting latent Mycobacterium tuberculosis
Mycobacterium tuberculosis
Mycobacterium tuberculosis is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis . First discovered in 1882 by Robert Koch, M...
infection. This test is an in vitro diagnostic aid that measures a component of cell-mediated immune reactivity
Cell-mediated immunity
Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells , antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen...
to M. tuberculosis. The test is based on the quantification of interferon-gamma
Interferon-gamma
Interferon-gamma is a dimerized soluble cytokine that is the only member of the type II class of interferons. This interferon was originally called macrophage-activating factor, a term now used to describe a larger family of proteins to which IFN-γ belongs...
(IFN-γ) released from sensitized lymphocytes in whole blood incubated overnight with purified protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
derivative (PPD) from M. tuberculosis and control antigens.
Tuberculin
Tuberculin
Tuberculin is the name given to extracts of Mycobacterium tuberculosis, M. bovis, or M. avium that is used in skin testing in animals and humans to identify a tuberculosis infection. Several types of tuberculin have been used for this, of which purified protein derivative is the most important....
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
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...
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
Venipuncture
In medicine, venepuncture, venopuncture or venipuncture is the process of obtaining intravenous access for the purpose of intravenous therapy or for blood sampling of venous blood. This procedure is performed by medical laboratory scientists, medical practitioners, some EMTs, paramedics,...
, 2) can be accomplished after a single patient visit, 3) assesses responses to multiple antigens simultaneously, and 4) 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.
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. There is need for further study of the utility of QFT in predicting the progression to active tuberculosis, particularly in children and immunocompromised hosts.
QuantiFERON-TB Gold
yesAccording to the U.S. Centers for Disease Control, 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 peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
s representing two M. tuberculosis proteins, ESAT-6
ESAT-6
ESAT-6, the 6 kDa early secretory antigenic target of Mycobacterium tuberculosis, is a secretory protein and potent T cell antigen. It is used in tuberculosis diagnosis by the whole blood interferon γ test QuantiFERON-TB Gold, in conjunction with CFP-10 and TB7.7.ESAT-6 has been shown to directly...
and CFP-10
CFP-10
CFP-10 also known as ESAT-6-like protein esxB or secreted antigenic protein MTSA-10 or 10 kDa culture filtrate antigen CFP-10 is a protein that is encoded by the esxB gene....
. 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 cell
White blood cell
White blood cells, or leukocytes , are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...
s 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 szulgaiMycobacterium szulgaiMycobacterium szulgai is a species of Mycobacterium. It is a Scotochromogen and is currently ungrouped. It is known to cause skin infections....
, Mycobacterium kansasiiMycobacterium kansasiiMycobacterium kansasii is a bacterium in the Mycobacterium family. The genus includes species known to cause serious diseases in mammals, including tuberculosis and leprosy, but this species is generally not dangerous to healthy people....
, and Mycobacterium marinumMycobacterium marinumMycobacterium marinum is a free-living bacterium, which causes opportunistic infections in humans.- History :Although Aronson isolated this mycobacterium in 1926 from a fish, it was not until 1951 that it was found to be the cause of human disease by Linell and Norden...
.
QuantiFERON-TB Gold In-Tube
On 10/10/2007 the US FDA gave approval for the Quantiferon TB Gold In Tube to be marketed in the USThe 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 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, http://www.cdc.gov/mmwr/pdf/rr/rr5905.pdf) 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.
• are unlikely to return for TST reading
nn
Medical facilities in the US using QFT can be found at http://www.cellestis.com/IRM/content/usa/contact_quantiferon.html. {Clicking on their column heading "State" twice will sort listings alphabetically by state. Likely more useful than their current default listing by alphabetical order of "Testing Facility" names}
Availability
In the United States, the test is widely available from state public health laboratories, hospitals, and commercial laboratoriesMedical laboratory
A medical laboratory or clinical laboratory is a laboratory where tests are done on clinical specimens in order to get information about the health of a patient as pertaining to the diagnosis, treatment, and prevention of disease.-Departments:...
.
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