QuantiFERON-TB Gold (Gamma Interferon) – ES153
🩸 Advanced TB Blood TestReport: 2nd Working Day
Sample Type: Blood (Special Tubes)
Test Code: ES153
The QuantiFERON-TB Gold Plus (QFT-Plus) is a modern and highly accurate blood test known as an Interferon-Gamma Release Assay (IGRA). It is used to detect infection with Mycobacterium tuberculosis, the bacterium that causes Tuberculosis (TB). This test is a superior alternative to the traditional skin prick (Mantoux) test.
✔ Detects both latent TB infection and active TB disease.
✔ Single blood draw; requires only one visit.
✔ Not affected by prior BCG vaccination, reducing the risk of false-positive results.
✔ An essential screening tool for healthcare workers and immunocompromised patients.
QuantiFERON-TB: The Modern Standard in TB Testing
Tuberculosis remains a significant global health concern. Accurate and rapid detection is key to controlling its spread. The QuantiFERON-TB Gold test represents a major advancement in TB diagnostics. Unlike the older Mantoux tuberculin skin test (TST), which involves injecting a substance into the skin and waiting 48-72 hours to check for a reaction, the QuantiFERON test is a simple, objective blood test.
How Does the Test Work?
The QuantiFERON test works by measuring the response of your immune system's T-cells to TB antigens. The process is as follows:
- A blood sample is collected into special tubes that contain specific TB bacterial proteins (antigens).
- If you have been exposed to TB bacteria, your immune system's T-cells will recognize these antigens and respond by releasing a substance called Interferon-gamma ($IFN-\gamma$).
- The laboratory measures the amount of $IFN-\gamma$ released. A significant amount indicates that your body has been "primed" by a previous TB infection.
This direct measurement of a specific immune response is what makes the test so accurate and reliable.
Key Advantages Over the Skin Test
- Unaffected by BCG Vaccine: The BCG vaccine is a common childhood vaccine for TB in countries like India. It can cause a false-positive reaction in the traditional skin test, suggesting infection where there is none. The QuantiFERON test uses antigens not present in the BCG vaccine, so it remains accurate even in vaccinated individuals.
- Single Visit: The skin test requires you to return to the clinic 2-3 days later for a reading. The QuantiFERON test requires only one visit for a blood draw.
- Objective Results: The skin test reading can be subjective and depends on the skill of the person measuring the reaction. The QuantiFERON test provides a quantitative, laboratory-measured result, removing potential for human error.
Latent TB vs. Active TB Disease
It's crucial to understand that a positive QuantiFERON result indicates a TB infection, but it does not, by itself, distinguish between latent TB and active TB disease.
- Latent TB Infection (LTBI): The person has TB bacteria in their body, but it's in an inactive or dormant state. They are not sick and cannot spread the bacteria to others. However, they are at risk of developing active TB disease later in life.
- Active TB Disease: The bacteria are active and multiplying, causing illness. The person may have symptoms like coughing, fever, and weight loss, and can spread the disease to others.
If your QuantiFERON test is positive, your doctor will perform further evaluations, such as a chest X-ray and clinical assessment, to determine if you have active TB disease that requires immediate treatment or latent TB that may require preventative therapy.
Frequently Asked Questions (FAQ)
Its main advantage is accuracy. It is not affected by the BCG vaccine, unlike the traditional skin test, which prevents false-positive results. It also requires only a single clinic visit.
No, fasting is not required for the QuantiFERON-TB Gold test. You can have your blood sample taken at any time.
A positive result means you have been infected with TB bacteria. It does not automatically mean you have active TB disease. Your doctor will order further tests, like a chest X-ray, to determine if the infection is latent (inactive) or active.
This test is recommended for people at high risk of TB exposure, such as healthcare workers, people who have been in close contact with someone with active TB, and patients who are about to start medications that suppress the immune system.
The test requires incubating the blood sample with TB antigens for a specific period (16-24 hours) to allow the immune cells to react and produce Interferon-gamma, which is then measured. This incubation step is why the process takes longer than a routine blood test.