Quantiferon Gold
Also known as: QFT-GIT, TB Gold
What Does Quantiferon Gold Measure?
QuantiFERON-TB Gold (QFT-GIT) is a blood test that measures the immune system's response to Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB). Specifically, it detects the release of interferon-gamma (IFN-γ), a signaling protein produced by white blood cells (T-lymphocytes) when they are exposed to TB-specific antigens — proteins unique to the TB bacterium. A small blood sample is mixed with these antigens in the laboratory, and the amount of IFN-γ released is measured to determine whether a person has been infected with TB.
Why Does Quantiferon Gold Matter?
Tuberculosis remains one of the world's leading infectious disease killers, and identifying latent TB infection (LTBI) — where a person carries the bacteria without active symptoms — is critical for preventing progression to active, contagious disease. Unlike the older tuberculin skin test (TST or PPD), QuantiFERON Gold is highly specific and does not produce false positives in people who have received the BCG vaccine, which is commonly given in many countries. It also requires only a single patient visit for a blood draw and produces results within 24 hours, making it a more convenient and accurate tool for TB screening in healthcare workers, immunocompromised individuals, recent immigrants from high-burden countries, and anyone at elevated risk of TB exposure.
Normal Ranges
Males
Negative: IFN-γ response < 0.35 IU/mL; Positive: ≥ 0.35 IU/mL
Females
Negative: IFN-γ response < 0.35 IU/mL; Positive: ≥ 0.35 IU/mL
Children
Same cut-off as adults (≥ 0.35 IU/mL = Positive); however, the test is less validated in children under 5 years — TST is preferred for very young children
Causes of High Levels
- Active tuberculosis disease (Mycobacterium tuberculosis infection)
- Latent tuberculosis infection (LTBI) — TB bacteria present but not causing active symptoms
- Infection with non-tuberculous mycobacteria such as M. kansasii or M. marinum (rare cross-reactivity)
- Recent close contact with a person who has active TB
- Prior occupational or environmental exposure to TB without development of disease
- Indeterminate result due to non-specific immune activation or laboratory handling issues (not a true positive)
Causes of Low Levels
- No prior exposure to Mycobacterium tuberculosis (true negative result)
- Severe immunosuppression (HIV/AIDS, organ transplant, high-dose corticosteroids) reducing T-cell response and causing false negatives
- Very recent TB infection (within 8 weeks of exposure) before immune sensitization has occurred
How to Improve Your Quantiferon Gold
Diet
- Maintain adequate protein intake (lean meats, legumes, eggs) to support a healthy immune system capable of mounting a measurable T-cell response
- Ensure sufficient vitamin D levels through fatty fish, fortified dairy, and sunlight exposure — vitamin D deficiency is associated with increased TB susceptibility
- Consume zinc-rich foods such as oysters, pumpkin seeds, and beef to support immune cell function and T-lymphocyte activity
- Eat antioxidant-rich fruits and vegetables (berries, leafy greens, bell peppers) to reduce systemic inflammation and support immune health
- Stay well-hydrated and maintain a balanced, whole-food diet to optimize overall immune function before testing
Supplements
- Vitamin D3: 1,000–4,000 IU/day if deficient — low vitamin D is linked to impaired immune response and higher TB risk; correct deficiency before testing if possible
- Zinc: 8–11 mg/day (RDA) — supports T-lymphocyte production; supplement only if dietary intake is inadequate
- Vitamin C: 500–1,000 mg/day — antioxidant support for immune function; may help optimize immune response accuracy
- Multivitamin with B-vitamins — B6 and B12 deficiency can impair immune cell function and affect test sensitivity
Related Biomarkers
Frequently Asked Questions
What is the difference between QuantiFERON Gold and the TB skin test (PPD)?
Both tests detect immune sensitization to TB bacteria, but they work differently. The tuberculin skin test (TST or PPD) involves injecting a small amount of TB protein under the skin and reading the result 48–72 hours later, requiring two clinic visits. QuantiFERON Gold is a single blood draw with results in 24 hours. The most important advantage of QFT is that it does NOT give false positives in people who have received the BCG vaccine, which is widely used outside the United States. This makes QuantiFERON more specific and reduces unnecessary treatment in vaccinated individuals.
Does a positive QuantiFERON Gold result mean I have active tuberculosis?
Not necessarily. A positive result means your immune system has been sensitized to TB bacteria, but it cannot distinguish between latent TB infection (LTBI) and active TB disease. In latent TB, the bacteria are dormant and you are not contagious and have no symptoms. Your doctor will order a chest X-ray and clinical evaluation to determine whether the infection is active or latent. Most people with a positive QFT have latent TB, which is treatable with antibiotics to prevent future activation.
Can the QuantiFERON test give a false negative result?
Yes. False negatives can occur in people with severely weakened immune systems — such as those with HIV/AIDS, organ transplant recipients on immunosuppressants, or those taking high-dose steroids — because their T-cells cannot produce a detectable interferon-gamma response. Very recent TB exposure (within 8 weeks) can also produce a false negative before the immune system has fully responded. In these high-risk populations, doctors may recommend repeat testing or use the TB skin test in combination to improve accuracy.