Quantiferon TB Gold / Interferon Gamma Release Assay (IGRA) Test
Quantiferon TB Gold / Interferon Gamma Release Assay (IGRA) Test
The Quantiferon TB Gold (QFT-G) Test is a modern blood test used to detect latent and active tuberculosis (TB) infections. It is an Interferon Gamma Release Assay (IGRA) that measures the immune system’s response to Mycobacterium tuberculosis, the bacteria responsible for TB. Unlike the traditional Tuberculin Skin Test (TST), the QFT-G test is more specific, does not require a return visit for results, and is not affected by prior BCG vaccination.
Tuberculosis is a highly contagious airborne disease that primarily affects the lungs but can also spread to other parts of the body, including the brain, kidneys, and spine. It spreads when an infected individual coughs or sneezes, releasing airborne droplets containing the Mycobacterium tuberculosis bacteria. While some people develop active TB with symptoms such as persistent cough, night sweats, weight loss, and fever, others may carry the bacteria in a latent form, showing no symptoms but still at risk of developing active TB later.
TB remains a major global health concern, particularly in low-income and high-burden countries. According to the World Health Organization (WHO), TB is one of the top 10 causes of death worldwide. Early detection and treatment are crucial in preventing the spread of TB and reducing its impact on public health.
This test is widely used in TB screening programs, especially for healthcare workers, individuals at high risk of TB exposure, and immunocompromised individuals.
What is the Quantiferon TB Gold Test Used For?
- Detecting latent TB infections (LTBI): Identifies individuals who have been exposed to TB bacteria but do not show active symptoms.
- Screening individuals at high risk of TB: Especially recommended for healthcare workers, travelers to high TB-endemic areas, immunocompromised patients (HIV, organ transplant recipients), and close contacts of TB-positive individuals.
- Differentiating between TB infection and BCG vaccination effects: Unlike the skin test, QFT-G is not influenced by previous BCG vaccination.
Aiding in active TB diagnosis: Used alongside clinical evaluations and imaging to confirm TB in symptomatic patients.
Symptoms of Tuberculosis
A healthcare provider may recommend this test if a patient presents with
Persistent cough lasting more than two weeks
Unexplained weight loss
Night sweats and fever
Fatigue and general weakness
Chest pain and difficulty breathing
History of close contact with a person diagnosed with TB
Preparation for the Test
No fasting is required for the test. Inform your doctor about any immune-suppressing medications you may be taking, as they could affect test results. Blood is collected via a standard venous draw and sent for laboratory analysis.
Interpretation of Test Results
FAQs
How does the Quantiferon TB Gold Test work?
The test measures interferon-gamma release in response to TB-specific antigens. A strong immune response suggests past or present TB exposure.
How is this test different from the Tuberculin Skin Test (TST)?
Unlike TST, QFT-G does not require a second visit and is not affected by prior BCG vaccination, reducing false positives.
Can this test distinguish between active and latent TB?
No, a positive result only indicates TB infection. Additional tests are needed to determine if TB is active or latent.
How long does it take to get results?
Results are typically available within 3 to 5 days.
What should I do if my test result is positive?
Consult a healthcare provider for further evaluation, including chest X-ray, sputum analysis, and clinical assessment.
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