Test ID: QTBG
Mycobacterium tuberculosis Infection Determination by QuantiFERON-TB Gold, Blood
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Indirect test for Mycobacterium tuberculosis complex infection (latent tuberculosis infection and active disease)
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
Enzyme-Linked Immunosorbent Assay (ELISA)
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Mycobacterium tuberculosis (MTB)
Purified Protein Derivative (PPD)
QuantiFERON-TB Gold
Tubercle Bacilli: Mycobacterium tuberculosis
Tuberculosis (TB)
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube:
Standard Altitude: QuantiFERON-QTB Gold In-Tube Collection Kit (Supply T628)
High Altitude: QuantiFERON High Altitude Collection Kit (Supply T649)
Collection Instructions:
1. Special collection, incubation, and centrifugation procedures must be followed.
2. Prepare and transport specimen per instructions in Mycobacterium tuberculosis Infection Determination by QuantiFERON in Special Instructions.
Forms: If not ordering electronically, submit a Microbiology Request Form (Supply T244) with the specimen.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross OK |
| Lipemia | Mild OK; Gross OK |
| Icterus | NA |
| Other | Specimen submitted not following kit guidelines |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole blood | Refrigerated | 28 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Latent tuberculosis infection (LTBI) is a noncommunicable, asymptomatic condition that persists for many years in individuals and may progress to tuberculosis disease. The main purpose of diagnosing LTBI is to consider medical treatment for preventing active tuberculosis disease. Until recently, the tuberculin skin test (TST) was the only method available for diagnosing LTBI. Unfortunately, the TST is a subjective test that can be falsely positive for individuals who have been vaccinated with Bacille Calmett-Guerin (BCG), are infected with other mycobacteria than Mycobacterium tuberculosis complex, or due to other factors such as a digital palpitation error when reading the test.
The QuantiFERON-TB Gold In-Tube test is a measure of cell-mediated immune response to antigens simulating the mycobacterial proteins ESAT-6, CFP-10, and TB7.7. Individuals infected with Mycobacterium tuberculosis complex organisms including Mycobacterium tuberculosis, Mycobacterium bovis, Mycobacterium africanum, Mycobacterium microti, and Mycobacterium canetti usually have lymphocytes in their blood that recognize these specific antigens. The recognition process involves the generation and secretion of the cytokine, gamma interferon (IFN-gamma). The detection and quantification of IFN-gamma by enzyme-linked immunosorbent assay (ELISA) is used to identify in vitro responses to TB antigens that are associated with Mycobacterium tuberculosis complex infection. The ESAT-6, CFP-10, and TB7.7 antigens are absent from the Mycobacterium bovis BCG strains and from most nontuberculous mycobacteria with the exception of Mycobacterium kanasii, Mycobacterium szulgai, and Mycobacterium marinum. Numerous studies have demonstrated that ESAT-6, CFP-10, and TB7.7 stimulate IFN-gamma responses in T cells from individuals infected with Mycobacterium tuberculosis but usually not from uninfected or BCG-vaccinated persons without disease or risk for LTBI.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Negative
Interpretation Provides information to assist in interpretation of the test results
A positive result indicates that Mycobacterium tuberculosis infection is likely. However, positive reactivity to proteins present in other mycobacteria such as Mycobacterium kansasii, Mycobacterium szulgai, and Mycobacterium marinum may cause false-positive results.
A positive QuantiFERON-TB Gold result should be followed by further medical and diagnostic evaluation for tuberculosis disease (eg, acid-fast bacilli smear and culture, chest x-ray).
QuantiFERON-TB Gold is usually negative in individuals vaccinated with Mycobacterium bovis Bacille Calmett-Guerin.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
A positive QuantiFERON-TB Gold result may not indicate infection with Mycobacterium tuberculosis; false positives do occur.
A negative QuantiFERON-TB Gold result does not preclude the possibility of Mycobacterium tuberculosis infection or tuberculosis disease. Falsely-negative results can be due to the stage of infection (eg, specimen drawn prior to the development of cellular immune response), comorbid conditions that affect immune functions, or other individual immunological factors.
A false-negative QuantiFERON-TB Gold result can be caused by incorrect blood specimen drawn or improper handling of the specimen affecting lymphocyte function. Blood must be incubated with stimulation antigens within 16 hours of draw. Delay in incubation may cause false-negative or indeterminate results.
The effect of lymphocyte count on reliability is unknown. Lymphocyte counts may vary from person to person. The minimum number required for a reliable result has not been established.
QuantiFERON-TB Gold has been evaluated with specimens from patients with culture-confirmed active tuberculosis and from apparently healthy adults with and without identified risk factors for Mycobacterium tuberculosis infection.
The performance of QuantiFERON-TB Gold has not been evaluated in specimens from:
-Individuals with impaired or altered immune functions (HIV infections, transplant patients, those receiving immunosuppressive drugs such as corticosteroids) and those with other clinical conditions (eg, diabetes, hematological disorders)
-Individuals younger than 17 years old
-Pregnant women
The most recent Centers for Disease Control and Prevention recommendations for diagnosis of Mycobacterium tuberculosis infections (including disease) and selecting persons for testing can be found at http://www.cdc.gov/nchstp/tb.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Mori T, Sakatani M, Yamagishi F, et al: Specific detection of tuberculosis infection: an interferon-gamma-based assay using new antigens. Am J Respir Crit Care Med 2004:170;59-64
2. Kang YA, Lee HW, Yoon HI, et al: Discrepancy between the tuberculin skin test and the whole blood interferon gamma assay for the diagnosis of latent tuberculosis infection in an intermediate tuberculosis burden country. JAMA 2005:293;2756-2761
3. Ferrara G, Losi M, Meacci M, et al: Routine hospital use of a commercial whole blood interferon-gamma assay for tuberculosis infection. Am J Respir Crit Care Med 2005 as doi:10.1164/rccm.200502-1960C
Method Description Describes how the test is performed and provides a method-specific reference
The QuantiFERON-TB Gold In-Tube test utilizes peptide cocktail simulating ESAT-6, CFP-10, and TB7.7 proteins, which are used to stimulate T cells in whole heparinized blood during incubation. The test is performed in 2 stages. First, 1 mL of whole blood is collected into each of 3 collection tubes: Nil Control tube, TB Antigen tube, Mitogen tube. Tubes are incubated at 37 degrees C within 16 hours of collection. Following a 16 to 24 hour incubation period, the tubes are centrifuged and the plasma is used to test for the amount of gamma interferon (IFN-gamma) present, measured by enzyme-linked immunosorbent assay.
A test is considered positive for an IFN-gamma response to the TB Antigen tube that is significantly above the negative control (Nil tube) value (IU/mL). The mitogen-stimulated plasma sample (Mitogen tube) serves as an IFN-gamma positive control for each sample tested. A low response to mitogen (<0.5 IU/mL) is an indeterminate result when a blood sample also has a negative response to the TB antigens. This pattern may occur with insufficient lymphocytes, reduced lymphocyte activity due to prolonged specimen transport or improper specimen handling, or inability of the patient's lymphocytes to generate IFN-gamma. The negative (Nil) sample adjusts for background, heterophile antibody effects, or non-specific IFN-gamma in blood samples. The IFN-gamma level of the negative control is subtracted from the IFN-gamma level for the TB Antigen tube and Mitogen tube. (Package insert: QuanitFERON-TB Gold (In-Tube Method), Cellestis Limited, Carnegie, Victoria, Australia, document number 05990301B, January 2007)
Note: Tuberculosis Antigen IU/mL value is reported (TB Ag IU/mL Value). This information may be required for certain Centers for Disease Control and Prevention (CDC) reporting forms (eg, Form I-693).
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Friday
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
86480
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 83896 | M. tuberculosis by QuantiFERON, B | 45323-3 |
| 32272 | Tuberculosis Antigen Value | 46217-6 |
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