Sign in →

Test Code 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


Specimen Required


Supplies:

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.


Specimen Minimum Volume

1 mL per tube (3 tubes)

Specimen Stability Information

Specimen Type Temperature Time
Whole blood Refrigerated 28 days

Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

Specimen submitted not following kit guidelines

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), who 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 M tuberculosis complex organisms including M tuberculosis, M bovis, M africanum, M microti, and M 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 M tuberculosis complex infection. The ESAT-6, CFP-10, and TB7.7 antigens are absent from the M bovis BCG strains and from most nontuberculous mycobacteria with the exception of M kanasii, M szulgai, and M marinum. Numerous studies have demonstrated that ESAT-6, CFP-10, and TB7.7 stimulate IFN-gamma responses in T cells from individuals infected with M tuberculosis, but usually not from uninfected or BCG-vaccinated persons without disease or risk for LTBI.

Reference Values

Negative

Interpretation

This is a qualitative test. The TB Antigen (Ag)-nil IU/mL value should not be used to differentiate active from latent disease or to monitor disease progression or response to therapy.

Diagnosis or exclusion of tuberculosis (TB) and assessing the probability of latent tuberculosis infection (LTBI), require a combination of epidemiologic, historical, clinical, radiologic, and additional laboratory findings (eg, mycobacterial smear and/or culture) be taken into account when interpreting QuantiFERON-TB Gold results.

 

The nil value is used to determine the background, circulating interferon-gamma level in the patient. For the QuantiFERON-TB Gold test to be valid, the nil value must be less than or equal to 8.0 IU/mL.

 

The mitogen minus nil value is used to assure that the patient is able to produce an interferon-gamma response to a universal stimulant (phytohemagglutinin). For the QuantiFERON-TB Gold test to be valid, the mitogen value must be at least 0.5 IU/mL higher than the nil value.

 

The QuantiFERON-TB Gold test is considered positive if the interferon-gamma response in the TB antigen minus nil value is at least 0.35 IU/mL.

Clinical Reference

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 Sep 1;172(5):631-635

Day(s) and Time(s) Performed

Monday through Friday, 9 a.m.

Analytic Time

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

LOINC Code Information

Test ID Test Order Name Order LOINC Value
QFT3 QuantiFERON-TB Gold In-Tube, B 71775-1

 

Result ID Test Result Name Result LOINC Value
QFTQ QuantiFERON-TB Gold Result 71773-6
DEXQ1 TB Ag minus Nil Result 64084-7
DEXQ3 Mitogen minus Nil Result 71774-4
DEXQ4 Nil Result 71776-9

Forms

If not ordering electronically, complete, print, and send a General Request Form (T239) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/general-request-form.pdf)