What this test measures
QuantiFERON-TB Gold Plus (QFT-Plus) is the most widely used commercial IGRA. It uses whole blood collected into 4 specialised tubes: nil (negative control), TB1 (CD4+ T-cell antigens), TB2 (CD4+ and CD8+ T-cell antigens), and mitogen (positive control). After overnight incubation, interferon-gamma in each tube is measured by ELISA. The TB-specific antigens (ESAT-6, CFP-10) are absent from BCG and most non-tuberculous mycobacteria, making the test highly specific for M. tuberculosis complex exposure.
The TB2 tube's inclusion of CD8+ responses improves sensitivity in HIV-infected and recently exposed individuals — an upgrade from the original QuantiFERON-TB Gold.
Why it matters
Latent TB infection (LTBI) affects an estimated 35–40% of Indian adults. Treating high-risk LTBI before progression to active disease is a central strategy in NTEP's TB elimination targets. QuantiFERON-TB Gold Plus is widely used in private healthcare in India for:
- Pre-employment screening of healthcare workers. - People living with HIV (TPT eligibility). - Household contacts of confirmed TB cases. - Pre-biologic, pre-transplant, pre-immunosuppression evaluation. - Migrants and travellers from high-burden countries entering low-burden countries.
Because it is unaffected by BCG vaccination, QFT-Plus avoids the major false-positive problem of the tuberculin skin test in Indian patients, all of whom received BCG at birth.
How to prepare
No fasting required. Whole blood is collected into the 4 specialised QFT-Plus tubes (nil, TB1, TB2, mitogen). Tubes must be shaken to mix with the antigens and incubated within 16 hours of collection. Inform the lab of any major immunosuppressive medications (steroids, biologics, chemotherapy) — they can blunt the response.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| TB1 or TB2 minus Nil (IU/mL)[1][2] | < 0.35 IU/mL = negative | Negative — no immune evidence of M. tuberculosis exposure. Does not exclude very recent infection (test in 8 weeks if exposed) or active TB in advanced immunosuppression. | ≥ 0.35 IU/mL = positive — immune sensitisation to TB present. Distinguish active TB from latent TB clinically; start TPT for latent TB in eligible individuals. |
| Mitogen control (IU/mL) | ≥ 0.5 IU/mL above nil | Failed mitogen control — immune response too weak; result is indeterminate. Common in immunosuppression. Repeat the test or use TST. | — |
QFT-Plus result interpretation
| Pattern | Interpretation |
|---|---|
| TB1/TB2 ≥ 0.35 + Mitogen OK | Positive — TB exposure |
| TB1/TB2 < 0.35 + Mitogen ≥ 0.5 | Negative — no exposure (or very recent / immunosuppressed) |
| TB1/TB2 < 0.35 + Mitogen < 0.5 | Indeterminate — repeat or use TST |
| Nil > 8.0 | Indeterminate — high background; repeat |
Frequently asked questions
How is QFT-Plus different from older IGRA versions?
The QFT-Plus version adds a TB2 tube containing antigens that stimulate CD8+ T cells, improving sensitivity in HIV-infected and recently exposed people. The older QuantiFERON-TB Gold lacked this.
Does my BCG vaccine affect the result?
No. The antigens used (ESAT-6, CFP-10) are absent from BCG. This is a major advantage over the tuberculin skin test for Indian patients, who all received BCG at birth.
Can QFT-Plus tell me if I have active TB?
No. A positive QFT-Plus confirms TB exposure but cannot distinguish active from latent infection. Active TB diagnosis still requires symptoms review, chest X-ray, and microbiological tests (CBNAAT, smear, culture).
Is QFT-Plus available under NTEP?
It is widely used in private healthcare in India and increasingly in tertiary public hospitals. The tuberculin skin test is more commonly used in NTEP's routine TPT pathway; either test is acceptable.
What if the result is indeterminate?
Indeterminate results occur when the mitogen control fails (immunosuppression) or the nil tube is very high (high background activity). Repeat the test or use the tuberculin skin test.
How long does the report take?
Typically 24–48 hours. The blood must incubate for 16–24 hours before the ELISA step.
Will I need treatment if positive?
A positive QFT-Plus prompts evaluation for active TB. If active disease is ruled out, TB preventive treatment (TPT) is offered to high-risk individuals — typically 3HP (rifapentine + isoniazid weekly for 3 months) or 6H (isoniazid daily for 6 months).
Related Tuberculosis / Mycobacterial tests
Tests commonly ordered alongside QUANTIFERON - TB, or that help interpret an unexpected result.
Sources & references
- CDC — Tuberculosis Testing · accessed 2026-05-30T00:00:00.000Z
- WHO — Latent TB Infection Guidelines · accessed 2026-05-30T00:00:00.000Z
- NTEP TB Preventive Treatment Guidelines · accessed 2026-05-30T00:00:00.000Z
- QuantiFERON-TB Gold Plus product information · accessed 2026-05-30T00:00:00.000Z
Book with Zelnoo
Get your QUANTIFERON - TB test done at home — transparent prices, NABL-accredited labs.
Zelnoo lets you compare diagnostic test prices across NABL-accredited labs in Mumbai & Thane, book a free home phlebotomist visit, and receive digital reports in 24–48 hours into a consent-first report vault. No subscriptions, no membership fees — pay only for the test you book.
Book QUANTIFERON - TB now