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Test ID QFT3 QuantiFERON-TB Gold In-Tube for Detection of Latent Tuberculosis, Blood

Useful For

Indirect test for Mycobacterium tuberculosis complex infection (latent tuberculosis infection)

Method Name

Enzyme-Linked Immunosorbent Assay (ELISA)

Reporting Name

QuantiFERON-TB Gold In-Tube, B

Specimen Type

Whole blood

Container/Tube:

Standard Altitude: QuantiFERON-QTB Gold In-Tube Collection Kit (T628)

High Altitude: QuantiFERON High Altitude Collection Kit (T649)

Collection Instructions:

1. Special collection, incubation, and centrifugation procedures must be followed.

2. Prepare and transport specimen per QuantiFERON-TB (QTB) Gold Collection and Processing Instructions (T688); available in Special Instructions.

Forms: If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

Microbiology Test Request Form (T244) (http://www.mayomedicallaboratories.com/it-mmfiles/microbiology_test_request_form.pdf)

General Test Request Form (T239) (http://www.mayomedicallaboratories.com/it-mmfiles/general-request-form.pdf)

Specimen Minimum Volume

1 mL per tube (3 tubes)

Specimen Stability Information

Specimen Type Temperature Time
Whole blood Refrigerated 28 days

Clinical Information

Latent tuberculosis infection (LTBI) is a noncommunicable, asymptomatic condition that persists for many years in individuals and may progress to tuberculosis (TB) 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, interferon-gamma (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

Negative

Cautions

False-positive QuantiFERON-TB Gold results may occur due to improper preanalytical processing of the QuantiFERON-TB Gold tubes, prior infection with certain other mycobacteria (eg, M marinum, M kansasii, M szulgai) or biologic variability. Positive results should be confirmed with other clinical, exposure, and laboratory findings.

 

TB antigen minus nil values between 0.35 IU/mL and 1.1 IU/mL may represent false-positive results in individuals at low risk for latent tuberculosis infection (LTBI). Repeat testing on a new specimen or testing for LTBI by an alternative method (eg, PPD: purified protein derivative) is recommended.

 

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 obtained prior to the development of cellular immune response), comorbid conditions that affect immune functions, other individual immunological factors, improper blood sample collection or handling of the specimen affecting lymphocyte function. Blood must be incubated with stimulation antigens within 12 hours of collection. 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.

 

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.

Day(s) Performed

Monday through Friday, 9 a.m.

Report Available

2 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

86480

NY State Approved

Yes