QuantiFERON Tuberculosis Blood Test (IGRA)

QuantiFERON TB Gold is a lab blood test that shows whether your immune system has reacted to the germ that causes TB. The current version, QuantiFERON-TB Gold Plus, is one of two TB blood tests approved in the US. It finds TB infection but cannot tell latent, inactive TB, which is not contagious, from active disease³. QuantiFERON was the first blood test of its kind, released in 2001⁶. FDA then approved QuantiFERON-TB Gold in 2005 and QuantiFERON-TB Gold In-Tube in October 2007, as CDC guidelines from 2010 record⁵. The test is made by the diagnostics company QIAGEN⁶.

What the numbers on the report mean is the next question. The guide to QuantiFERON results explained goes through each line.

An IGRA, or interferon-gamma release assay, is the type of TB blood test that QuantiFERON belongs to. Two IGRAs are approved and sold in the US, QuantiFERON-TB Gold Plus and T-SPOT.TB. Both measure the response to two TB proteins, ESAT-6 and CFP-10¹. CDC guidance from 2024 says the lab mixes the blood with peptides that mimic TB proteins, alongside control samples¹. White blood cells from an infected person respond by releasing interferon-gamma, and the test measures that response¹. The comparison of T-SPOT vs QuantiFERON sets the two side by side.

QuantiFERON tests for an immune response to Mycobacterium tuberculosis, which shows past or present infection rather than the germ itself. Its test proteins are found in the whole M. tuberculosis complex, including M. bovis, the cattle form of the germ. CDC guidelines from 2010 note that three other species carry the same proteins and may cause a false-positive result⁵. They are M. kansasii, M. szulgai and M. marinum⁵. CDC guidance from 2024 says specific immunity develops within six to eight weeks of infection in most people¹. Only then can the blood respond¹. Untreated advanced HIV or severe immune suppression, such as sepsis, can cause a false-negative result, the same 2024 CDC guidance warns¹. The page on how does a TB test work explains the immune reaction.

QuantiFERON-TB Gold Plus is the version of the test that uses four blood tubes: Nil, TB1, TB2 and Mitogen. The TB1 tube mainly picks up the CD4 T-cell response, and TB2 picks up both CD4 and CD8 responses.

QIAGEN states that TB-specific CD8 responses are found more often in active TB disease⁶. They can also be detected in people with HIV and in young children⁶. TB1 can still read higher than TB2, for example in TB of the lymph nodes or the pleura⁷. The page on QuantiFERON TB1 and TB2 antigen values explains the numbers.

The QuantiFERON blood test is done with a single blood draw at a clinic or lab. Blood goes into four 1 mL tubes, or into one heparin tube of at least 5 mL for the lab to divide. The tubes have to be incubated within 16 hours of the draw¹. Each tube is shaken 10 times after filling to dissolve the test proteins on its walls⁶. Blood in a single heparin tube can wait up to 12 hours at room temperature before transfer⁶. Refrigerated, it can wait up to 53 hours⁶. Labcorp asks for a needle and holder rather than a butterfly needle, and notes that each tube draws only 1 mL⁷. The page on the QuantiFERON blood draw covers what to expect.

A QuantiFERON test takes one visit for a blood draw, and results come within 24 hours or several days. The lab incubates the tubes for 16 to 24 hours before reading them. QIAGEN gives the ELISA reading as 24 to 28 hours from the draw⁶. Quest tells consumers to expect results in 2 to 3 business days⁸. The page on how long do QuantiFERON results take compares labs.

A QuantiFERON result tells you whether the lab found a TB immune response above the set cutoff. It is positive when TB1 or TB2 minus Nil is at least 0.35 IU/mL and at least 25% of Nil. Indeterminate means the Nil is above 8.0 IU/mL or the Mitogen response is too low, so no answer is possible⁴. A higher number does not mean a later stage or a greater chance of disease⁴. The lab turns the tube values into one final result of positive, negative or indeterminate⁴. CDC guidance from 2024 says a negative result means infection is unlikely but cannot be excluded¹. That is most true with TB symptoms or a weakened immune system¹. In QIAGEN clinical studies of QFT-Plus, the indeterminate rate was under 2.5% in active TB⁶. The page on a positive QuantiFERON result covers the next steps.

No: QuantiFERON and the skin test find the same infection, and neither is better for everyone. QuantiFERON needs one visit and is not changed by BCG. 2025 CDC guidance still prefers the skin test under age 5. The blood test is safe in pregnancy². CDC guidance from 2024 notes the skin test needs a return visit two to three days later to be read¹. CDC guidelines from 2010 allow either test, without preference, for recent contacts of someone with TB disease⁵. The same 2010 guidelines do not generally recommend testing with both⁵. Both can help when the first is negative and the risk is high⁵. The comparison of QuantiFERON vs PPD goes further.

A QuantiFERON test suits anyone who should get a TB test, and 2025 CDC guidance prefers a blood test for two groups. Those groups are people who had the BCG vaccine and people who may not come back for a second visit. QIAGEN states the test suits children, pregnant women and people with weak immune systems⁶. CDC guidance from 2024 names four higher-risk groups who should get tested³.

• People born in, or who often travel to, countries where TB is common
• People who live or lived in group settings such as shelters, prisons or jails
• People who recently spent time with someone with active TB disease
• People who work where TB is more likely to spread

CDC adds in that 2024 guidance that TB tests are generally not needed for people at low risk³. For a US immigration medical exam, CDC instructions from 2024 require an IGRA for every applicant aged 2 or older⁹. The TB blood test guide covers the skin test too.

These short answers cover BCG, cost, where to test, preparation, versions, accuracy and retesting.