QuantiFERON TB Gold
Label Mnemonic: QTB
Epic Lab Code: LAB4485
Downtime Form: A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery
Commercial Mail-out Laboratory
5231 RCP
356-8593
Specimen(s):
Whole Blood
Specimen Instructions:
Specimen collection performed only by Department of Pathology phlebotomists (outpatient & inpatient) or other staff trained in collection.

Contact Core Laboratory at (356-3527) or Mailouts at (356-8593) for the QuantiFERON-TB Plus Collection Kit.
Collection Medium:
QuantiFERON-TB Plus Collection Kit
Minimum:
1 mL whole blood per tube (all FOUR tubes required)
Rejection Criteria:
Specimens other than plasma in QTB collection vials.
Turn Around Time:
2 days upon receipt at reference laboratory
Reference Range:
Negative
Interpretive Data:
A single positive result by this test should not be used solely to diagnose latent tuberculosis (TB). Results should be used in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations.

Positive:
Interferon-gamma (IFN-gamma) response to Mycobacterium tuberculosis antigens detected, suggesting infection with M tuberculosis. Positive results in patients at low-risk for TB should be interpreted with caution and repeat testing on a new sample should be considered as recommended by the 2017 ATS/IDSA/CDC Clinical Practice Guidelines for Diagnosis of Tuberculosis in Adults and Children.(1) False-positive results may occur in patients with prior infection with M marinum, M szulgai, or M kansasii.

Negative:
No IFN-gamma response to M tuberculosis antigens was detected. Infection with M tuberculosis is unlikely. A single negative result does not exclude infection with M tuberculosis. In patients at high risk for M tuberculosis infection, a second test should be considered in accordance with the 2017 ATS/IDSA/CDC Clinical Practice Guidelines for Diagnosis of Tuberculosis in Adults and Children.

Indeterminate due to Low Mitogen Value:
Indeterminate due to a low IFN-gamma level in the mitogen (positive control) tube. This may occur due to a low lymphocyte count, reduced lymphocyte activity, or inability of the patient's lymphocytes to generate IFN-gamma.

Indeterminate due to High Nil value:
Indeterminate due to a high level of IFN-gamma in the Nil (negative control) tube. This may occur due to heterophile antibody effects or nonspecific, circulating IFN-gamma in the patient's blood sample. Repeat testing on a new specimen is suggested.
Comments:
Collection kit contains four tubes (Yellow, Gray, Green and Lavender).

Contact Core Laboratory at (356-3527) or Mailouts at (356-8593) for the QuantiFERON-TB Plus Collection Kit.

Cautions:
A negative QuantiFERON-TB Gold Plus (QFT-Plus) result does not preclude the possibility of Mycobacterium tuberculosis infection or tuberculosis disease. False-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, incorrect handling of the blood collection tubes following venipuncture, or other individual immunological factors. Additionally, heterophile antibodies or nonspecific interferon-gamma (IFN-gamma) production from other inflammatory conditions may mask specific responses to ESAT-6 or CFP-10 peptides.

A delay in incubation may cause false-negative or indeterminate results, and other technical parameters may affect the ability to detect a significant IFN-gamma response.

A positive QFT-Plus result should not be the sole or definitive basis for determining infection with M tuberculosis. Positive results should be followed by further medical evaluation for active tuberculosis disease (eg, acid-fast bacilli smear and culture, chest X-ray).

While ESAT-6 and CFP-10 are absent from all bacille Calmett-Guerin (BCG) strains and from most known nontuberculous mycobacteria, it is possible that a positive QFT-Plus result may be due to infection with M kansasii, M szulgai, or M marinum. If such infections are suspected, alternative tests should be performed.

The effect of lymphocyte count on reliability is unknown. Lymphocyte counts may vary over time for any individual person and from person to person. The minimum number required for a reliable result has not been established and may also be variable.

The predictive value of a negative QFT-Plus result in immunosuppressed patients has not been determined.

Children <17 & pregnant women-tested with disclaimer.

Useful For: Indirect test for Mycobacterium tuberculosis infection, to be used in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations.
Methodology:
Enzyme-Linked Immunosorbent Assay (ELISA)
CPT Code:
86480