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Test Code QN1TB QuantiFERON ®-TB Gold Plus, 1 Tube

Additional Codes

Epic: LAB13888

Quest: 36970

Specimen Required

Specimen Type: Whole blood, Lithium Heparin

Collection Container/Type: Green top (Lithium Heparin)

Submission Container/Tube: Green top (lithium heparin)

Specimen Volume: 6mL

Collection Instructions: 

  1. Collect a minimum of 6 mL of blood by venipuncture into a lithium heparin (green-top) tube.
  2. Gently mix by inverting the tube several times to dissolve the heparin. 
  3. Refrigerate at 2-8° C.

Additional Information:

  1. The Centers for Disease Control and Prevention (CDC) has provided guidance on clinical considerations for tuberculosis (TB) testing such as QuantiFERON®-TB Gold Plus in conjunction with COVID-19 mRNA vaccines. 
    CDC. Fast facts: Interferon-gamma release assays (IGRAs)-blood tests for TB infection. Published November 2011.

Specimen Minimum Volume

6 mL

Specimen Stability

Room temperature: Unacceptable

Refrigerated: 48 hours

Frozen: Unacceptable

Clinical Significance

This test is a blood-based interferon-gamma release assay (IGRA) used as an aid in the diagnosis of Mycobacterium tuberculosis infection. It is an immune response-based, indirect test for M tuberculosis infection (including disease) and is intended for use in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations. Additional testing is needed to determine if a person who has tested positive has latent tuberculosis (TB) infection or TB disease.

This in vitro diagnostic test uses a peptide cocktail simulating ESAT-6, CFP-10, and TB7.7 proteins to stimulate cells in heparinized whole blood. Detection of interferon-γ (IFN-γ) by ELISA is used to identify in vitro responses to those peptide antigens that are associated with Mycobacterium tuberculosis infection.

Guidelines recommend testing for individuals who 1) have been exposed to a person with latent or active TB, including the general population and healthcare workers; 2) are from TB-endemic countries, which include most countries in Latin America, the Caribbean, Africa, Asia, and Eastern Europe, and Russia; 3) work in high-risk settings, such as correctional facilities, long-term care (LTC) facilities, nursing homes, and homeless shelters; or 4) have HIV or have an injection drug substance use disorder [1].

All of these individuals can be tested with either a traditional tuberculin skin test (TST) or an IGRA. However, the American Thoracic Society (ATS), the Infectious Disease Society of America (IDSA), and the Centers for Disease Control and Prevention (CDC) jointly prefer an IGRA test for individuals who have been vaccinated against bacillus Calmette-Guérin (BCG) or are not likely to return for the follow-up portion of the TST (and in both cases are at least 5 years old and likely to have TB infection and are at low or moderate risk of disease progression, or in whom it has been determined that TB testing is necessary [1]. The QuantiFERON-TB Gold test has specificity >99% in low-risk individuals and sensitivity of 92% in individuals with active disease [2].

In contrast to the TST, IGRA testing for TB requires only 1 patient visit (instead of 2). Also, IGRAs are not associated with the booster phenomenon, in which previously infected individuals generate a false-positive on a TST. In addition, prior BCG vaccination does not generate a false-positive result. Note that for children aged 2 and above, either TST or IGRA can be used [3,4]

The CDC does not recommend dual testing with both a TST and an IGRA, unless the goal is to confirm a positive result, or when a high-risk individual's test results are negative and there is clinical suspicion of TB. In this clinical situation, dual testing is used for confirmatory purposes [4].

For more information about TST versus IGRA testing, please visit the QuantiFERON®-TB Gold FAQs page.

Note that when using QuantiFERON®-TB Gold Plus, blood samples must be processed within 16 to 48 hours after collection while white blood cells are still viable.

Reference Range

Negative

Rejection Due To

Sodium heparin (green-top) tubes • Gel-barrier lithium heparin tubes • QuantiFERON ®-TB Gold Plus 4 tube collection kit • Incubated specimens

Day(s) and Time(s) Performed

Daily

Report Available

2 - 3 days

Method Name

Immunoassay (IA)

CPT Code(s)

86480

Aliases

TB Gold,QFT Gold Plus,QFT TB,QFT Plus,IGRA