What Is the QuantiFERON-TB Gold Test?

The QuantiFERON-TB Gold Plus (QFT-Plus) is an Interferon-Gamma Release Assay (IGRA) — a blood test that measures the immune system's response to Mycobacterium tuberculosis antigens. It is the preferred TB screening method for the USCIS immigration medical examination, as recommended by the CDC Technical Instructions for Civil Surgeons.

Why QFT Is Preferred Over the Tuberculin Skin Test (TST)

The QuantiFERON-TB Gold test has several advantages over the traditional tuberculin skin test (TST/Mantoux):

• Single blood draw — no return visit required to read results
• Not affected by prior BCG vaccination (BCG does not cause false positives)
• More specific — fewer false positive results
• Results available in 1–2 business days
• No subjective reading — laboratory-based measurement

How the Test Is Performed

The QFT test requires a single blood draw performed on the day of your immigration medical exam appointment. The blood sample is sent to our laboratory and incubated with TB antigens. The laboratory measures the amount of interferon-gamma released by white blood cells in response to the antigens. All testing is performed on-site; no separate lab visit is required.

Understanding QFT Results

Negative (Non-Reactive): No TB infection detected. This is the expected result for most applicants.

Positive (Reactive): Indicates TB infection — either latent TB infection (LTBI) or active TB disease. A positive QFT requires a chest X-ray to evaluate for active TB disease.

Indeterminate: The test result is inconclusive. This can occur due to laboratory issues or immune system factors. An indeterminate result typically requires repeat testing.

What Happens If Your QFT Is Positive

A positive QuantiFERON-TB Gold result means you have been infected with TB bacteria at some point. It does not necessarily mean you have active TB disease. Your Civil Surgeon will order a chest X-ray to evaluate for active TB.

Latent TB infection (LTBI) — TB bacteria present but not causing active disease — is NOT a ground of inadmissibility. It does not prevent green card approval. Active TB disease is a Class A condition and requires treatment.

BCG Vaccination and QFT

Many applicants from countries where TB is prevalent received the BCG (Bacillus Calmette-Guérin) vaccine in childhood. Unlike the tuberculin skin test, the QuantiFERON-TB Gold test is not affected by prior BCG vaccination. BCG vaccination does not cause a positive QFT result, making it a more reliable screening tool for immigration applicants from high-TB-burden countries.

Documentation on Form I-693

TB testing results are documented in Part 3 of Form I-693 (Tuberculosis). Your Civil Surgeon records the QFT result, chest X-ray findings if applicable, and any follow-up evaluation. The completed form is sealed and submitted to USCIS.