Tuberculosis (TB) Blood Test (QuantiFERON)
The QuantiFERON TB blood test is a modern alternative to the tuberculin skin test that measures immune response to detect latent or active tuberculosis infection.
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What this test measures
The QuantiFERON-TB Gold Plus is an interferon-gamma release assay (IGRA) that measures the immune system's response to specific tuberculosis proteins. This in vitro diagnostic test uses a peptide cocktail of CD4+ and CD8+ T cell antigens to stimulate cells in heparinized whole blood, with interferon-gamma detection by ELISA to identify responses associated with Mycobacterium tuberculosis infection.
The test detects cell-mediated immune responses to peptide antigens that simulate mycobacterial proteins (ESAT-6 and CFP-10), which are absent from all BCG strains and most non-tuberculous mycobacteria except M. kansasii, M. szulgai, and M. marinum. A positive result does not distinguish between active and latent TB infection, as both forms can trigger the same immune response. The test is intended for use in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations.
Who should consider this test
You might consider this test if you are experiencing any of the following:
- Individuals who have been exposed to someone with active tuberculosis and need to determine if they have been infected with the TB bacteria.
- Healthcare workers, first responders, and those in high-risk occupations who require regular tuberculosis screening as part of their employment requirements.
- People who have received the BCG vaccine and need tuberculosis testing, as the QuantiFERON test is not affected by prior BCG vaccination unlike the traditional skin test.
- Patients who are unable to return for tuberculin skin test reading appointments, as the QuantiFERON requires only one laboratory visit for blood collection.
- Those who are immunocompromised or have conditions that may affect their ability to mount an immune response, where more precise testing may be beneficial.
- Individuals traveling to or immigrating from countries with high tuberculosis rates who need documentation of their TB infection status.
- People with symptoms suggestive of tuberculosis infection or disease who need evaluation as part of their diagnostic workup.
What to expect
Preparation
No fasting or special preparation is required. Individuals should inform their healthcare provider of any medications they are taking, particularly immunosuppressive drugs that might affect immune function.
Sample Type
A healthcare professional will collect a blood sample from a vein in the arm using a standard needle. The blood is collected into special tubes containing specific antigens that will stimulate an immune response if TB infection is present.
Collection
The blood draw typically takes just a few minutes at the laboratory location. The special collection tubes may take slightly longer to fill than standard blood collection tubes due to their unique design.
Turnaround
Test results are typically available within 2-5 business days after the laboratory receives the specimen.
Understanding your results
Results are reported as positive, negative, or indeterminate based on the amount of interferon-gamma produced in response to tuberculosis-specific antigens. A positive result suggests tuberculosis infection is likely, while a negative result indicates infection is not likely.
| Population | Reference Range | Notes |
|---|---|---|
| Adults and children | Negative: < 0.35 IU/mL | Standard cutoff for negative results |
| Adults and children | Positive: ≥ 0.35 IU/mL | Indicates likely TB infection |
| Adults and children | Borderline: 0.20-0.99 IU/mL | May require repeat testing for confirmation |
Reference ranges may vary by laboratory and individual factors. Results should be interpreted by a healthcare provider in the context of your overall health.
What does a “Low” result mean?
A negative result does not preclude the possibility of Mycobacterium tuberculosis infection or tuberculosis disease, as false negative results can occur due to the stage of infection, conditions that affect immune function, or improper specimen handling. Indeterminate results are rare (0% to 2.3% of all results) and may be caused by a compromised immune system or inappropriate specimen handling. An indeterminate result suggests possible preanalytic error or individual patient-related factors.
What does a “High” result mean?
A positive QuantiFERON-TB Gold Plus result indicates that Mycobacterium tuberculosis infection is very likely. However, the test cannot distinguish between active tuberculosis disease and latent tuberculosis infection. Positive results should not be the sole basis for determining TB infection and should be followed by further medical evaluation for active tuberculosis disease. False-positive results may occur due to improper specimen processing, prior infection with certain other mycobacteria, or biological variability.
Privacy & confidentiality
All QuantiFERON tuberculosis test results are kept strictly confidential and protected under HIPAA regulations. Results are not automatically shared with your personal physician, added to your medical records, or reported to insurance companies unless you specifically request it. No doctor visit is required to order this test.
Frequently asked questions
Related tests
CPT Code: 86480
This test may not be available in: NY, NJ, RI
This page is for informational purposes only and does not constitute medical advice. Always consult with a healthcare provider regarding any health concerns. LevelPanel does not diagnose, treat, or prescribe.
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