Test Description
The QuantiFERON-TB Gold test is a modern blood test designed to detect infection with Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB).
This test is classified as an interferon-gamma release assay (IGRA), which measures the immune response to specific TB antigens.
The QuantiFERON-TB Gold test is recognized for its high specificity and sensitivity, making it a reliable alternative to the traditional tuberculin skin test (TST) for diagnosing latent tuberculosis infection (LTBI).
How Quantiferon -TB Gold; Gamma Interferon test works
The test utilizes three specialized blood collection tubes:
- Nil Control: Measures background levels of interferon-gamma.
- TB Antigen Tube: Contains specific TB antigens that stimulate an immune response.
- Mitogen Control: A positive control to ensure the immune system can respond.
When a patient’s blood is exposed to these antigens, T cells in the blood release interferon-gamma if they have been sensitized by previous exposure to TB. This immune response is quantified and interpreted to determine whether the patient has LTBI.
Indications of the Quantiferon-TB Gold; Gamma Interferon Test
The QuantiFERON-TB Gold test is recommended for:
- Individuals at high risk for TB, including healthcare workers, immunocompromised patients, and those with a history of exposure.
- Screening before starting immunosuppressive therapy.
- Evaluating suspected cases of TB where chest X-rays and clinical assessments are inconclusive.
Patient Preparation/Instructions
Patients do not require any special preparation before the test. However, it is advisable to inform healthcare providers about any recent infections or vaccinations.
It is also recommended to avoid antibiotics or immunosuppressive medications prior to testing when possible.
Typical Reference Values
- Negative Result: Indicates no evidence of TB infection.
- Positive Result: Suggests LTBI; further evaluation may be necessary to rule out active TB.
- Indeterminate Result: Indicates that the test could not definitively confirm or exclude TB infection, often requiring retesting or additional diagnostic evaluations.
Turnaround Time
Results from the QuantiFERON-TB Gold test are generally available within 24 to 48 hours after the blood sample is collected.
Advantages Over Traditional Testing
- Single Visit: Unlike the TST, which requires two visits, QuantiFERON testing can be completed in one appointment.
- No Reading Variability: Results are objective and do not require interpretation by a healthcare provider.
- BCG Vaccination Compatibility: The test is not affected by previous Bacillus Calmette-Guerin (BCG) vaccination, reducing false positives common with TST.
Limitations
While QuantiFERON-TB Gold is highly effective, it cannot differentiate between active and latent TB infection. Therefore, it should be used in conjunction with clinical assessments and other diagnostic tools. Indeterminate results may occur in individuals with compromised immune systems or improper sample handling.
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To order the QuantiFERON-TB Gold test, please click the ‘Order Test’ button and add it to your cart.
