The essentials

QuantiFERON-TB Gold Plus is a blood test that shows whether your immune system has met the tuberculosis (TB) germ. A positive result usually means TB infection, most often the latent kind that is not contagious and causes no symptoms; it does not mean you are sick. A negative result makes infection unlikely, and an indeterminate result means the test could not give an answer and is usually repeated.

How do I read my QuantiFERON test results?

The test mixes your blood with TB proteins and measures the interferon-gamma your white blood cells release[1]. In this fictitious US report, four numbers lead to one word: positive, negative or indeterminate.

Fictitious example of a lab report line (United States format)
TestResultReference rangeFlag
Nil0.08 IU/mL≤8.00 IU/mL-
TB1 Antigen minus Nil0.52 IU/mL<0.35 IU/mLH
TB2 Antigen minus Nil0.61 IU/mL<0.35 IU/mLH
Mitogen minus Nil7.85 IU/mL≥0.50 IU/mL-
QuantiFERON-TB Gold PlusPositiveNegativeA
  1. Nil: the background tube, with no TB protein. It must be 8.0 IU/mL or less for the test to be valid; it is subtracted from the other tubes[6].
  2. TB1 minus Nil: the response of CD4 helper T cells to TB proteins. TB2 minus Nil: the same, plus CD8 T cells[6]. A tube counts as positive at 0.35 IU/mL or more, if that is also at least 25% of the Nil value[5]. Here both tubes pass.
  3. Mitogen minus Nil: the positive control. It shows your cells can respond at all, and must be at least 0.50 IU/mL[6].
  4. Final result, flag A (abnormal): "M. tuberculosis infection likely"[5]. Values of 0.52 and 0.61 are low positives, close to the cut-off; how much weight they carry depends on your risk of exposure.

Four numbers and one word that does not say whether you are ill? BloodSense explains each line of your report and helps you prepare questions for your doctor.

Get my QuantiFERON result explained

What is the QuantiFERON test used for?

It answers one question: has this person been infected with the TB germ? It is used wherever the tuberculin skin test (TST, or PPD) is, including contact tracing, recent immigrants and health worker screening[8]. It is also common before treatments that weaken the immune system, such as biologics for rheumatoid arthritis or Crohn's disease, because latent TB can wake up.

US guidelines recommend a TB blood test rather than a skin test for people aged 5 and over who were vaccinated with BCG or are unlikely to come back for a skin test reading; they suggest it for most others aged 5 and over, and suggest the skin test for healthy children under 5[3]. The World Health Organization also accepts the skin test and newer antigen-based skin tests[4].

What the test cannot do: tell latent infection from active disease, or measure how well treatment works[6][9]. The disease itself, its symptoms and its treatment are covered in our guide to tuberculosis symptoms and tests.

What are the QuantiFERON cut-off values?

There is no "normal range": the lab software applies the manufacturer's rules[6].

QuantiFERON-TB Gold Plus interpretation rules (IU/mL)
ValuesResultSource
Nil ≤8.0, and TB1 or TB2 minus Nil ≥0.35 and ≥25% of NilPositiveQIAGEN[5]
Nil ≤8.0, both TB tubes below that threshold, Mitogen minus Nil ≥0.50NegativeQIAGEN[5]
Nil ≤8.0, both TB tubes below that threshold, Mitogen minus Nil <0.50Indeterminate (low mitogen)QIAGEN[5]
Nil >8.0Indeterminate (high Nil)Quest Diagnostics, University of Iowa laboratory[6][7]
TB response 0.15-0.35 or 0.35-0.70 (research categories, not used on reports)"Borderline" or "low positive"Dutch contact study[10]

In that study, most borderline and low-positive results reflected a real response to TB rather than test noise[10]. A bigger number does not mean a worse or more advanced infection, nor a higher chance of falling ill[6]. Your laboratory's report and your doctor's reading prevail.

What does a positive QuantiFERON result mean?

"A positive test result usually means TB infection"[1]. The next step is a check for active disease, with a chest X-ray and, if needed, sputum tests[1][2]. Possible explanations, from most to least frequent:

  • Common Latent TB infection: the germ is dormant, you feel well, the X-ray is normal and you cannot pass it on[11]. Without treatment, about 5 to 10% of infected people develop TB disease over their lifetime; treatment is about 90% effective and now usually lasts 3 to 4 months[11].
  • Possible A false positive close to the cut-off: in serial testing studies, about 20 to 60% of positives turned negative on retesting[9]. For people at low risk who were tested anyway, for example for a job, US guidelines suggest a second test and consider them infected only if both are positive[3].
  • Possible Active TB disease: more likely with symptoms such as a long cough, fever, night sweats or weight loss[12].
  • Rare Related bacteria: infection with M. kansasii, M. szulgai or M. marinum can also turn the test positive[7].

The BCG vaccine does not normally cause a positive QuantiFERON[8][9]. Keep perspective: in follow-up studies, more than 95% of people with a positive TB blood test or skin test did not develop TB disease[9].

What does a negative QuantiFERON result mean?

"TB infection is unlikely, but cannot be excluded"[1]. A negative test can be falsely reassuring in these situations[1][7]:

  • Common Recent exposure: blood drawn before the immune response has developed.
  • Possible A weakened immune system: HIV infection, immune-suppressing drugs or other illnesses that dampen T cells.
  • Possible Sample handling: a delay before incubation can cause false negatives.
  • Rare Severe TB disease itself, which can blunt the response.

With symptoms, HIV or a recent exposure, more tests may follow anyway[2].

What does an indeterminate QuantiFERON result mean?

It is not a hidden positive: the control tubes did not allow a conclusion[1][5]. The report often says which control failed:

  • Common Handling problems: tubes not incubated in time, mixed too little or too hard, or kept at the wrong temperature[6].
  • Possible Low mitogen: a low lymphocyte count or lymphocytes that respond poorly[7], for example with high-dose steroids or other immune-modulating drugs[6]. In people with HIV, about 8% of QuantiFERON results were indeterminate in pooled studies[9].
  • Rare High Nil: heterophile antibodies or interferon already circulating in the blood, as in some inflammatory conditions[7].

The usual answer is a repeat test on a new sample, or a skin test[1][7]. If your complete blood count shows low lymphocytes, mention it.

What can affect a QuantiFERON result?

No preparation or fasting is needed[8]. Most problems happen in the tubes:

  • Each tube is filled to its black line (0.8 to 1.2 mL) and shaken about 10 times, not too hard[8].
  • Tubes stay at room temperature and reach the lab in time: CDC gives a window of 8 to 32 hours after collection for processing[1].
  • Tell the person ordering the test about steroids, biologics, chemotherapy or a recent illness or vaccine[6].
  • Mention a BCG vaccine or a past positive TB test, and keep a written record of any positive result[2].
  • After a recent exposure, ask whether a repeat test is planned later[7].

For the draw itself, see what to expect at a blood draw.

When should I see a doctor about my QuantiFERON result?

When to see a doctor

  • Emergency: call 911 if you cough up a lot of blood, or have severe trouble breathing or chest pain.
  • Within 24 to 48 hours for a cough lasting 3 weeks or more, coughing up blood-streaked sputum, fever, night sweats or unplanned weight loss, whatever your result[12].
  • At your next appointment for a positive result without symptoms, to plan the chest X-ray and discuss treatment, or for an indeterminate result.

Questions to ask your doctor

  1. Is my result clearly positive, or close to the 0.35 cut-off?
  2. Given my risk of exposure, should the test be repeated or confirmed with another test?
  3. Do I need a chest X-ray, and when?
  4. If I have latent TB, which treatment do you suggest?

Frequently asked questions

Can the BCG vaccine make my QuantiFERON positive?

No. Its TB proteins are absent from all BCG strains, so the blood test is preferred after BCG[2][7].

How long does it take to get QuantiFERON results?

Results can be available within 24 hours, but often take several days, depending on the laboratory[1].

Will my QuantiFERON stay positive after treatment?

It may. The test is not used to monitor treatment[6], and future TB tests can still come back positive, which is why CDC suggests keeping a written record[2]. During treatment, doctors may watch your liver enzymes.

Is QuantiFERON more accurate than T-SPOT.TB?

Both are acceptable. In a major review, T-SPOT.TB detected active TB slightly more often (about 90% versus 80%), and both were more than 95% specific in low-TB countries[9].

  1. Centers for Disease Control and Prevention. Interferon Gamma Release Assay. Tuberculosis (TB), clinical testing and diagnosis. cdc.gov (accessed November 10, 2026)
  2. Centers for Disease Control and Prevention. Testing for Tuberculosis: Blood Test. cdc.gov (accessed November 10, 2026)
  3. Lewinsohn DM, Leonard MK, LoBue PA, et al. Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children. Clin Infect Dis. 2017;64(2):e1-e33. doi:10.1093/cid/ciw694 (accessed November 10, 2026)
  4. World Health Organization. WHO consolidated guidelines on tuberculosis. Module 3: diagnosis. Tests for tuberculosis infection. Geneva: WHO; 2022. who.int (accessed November 10, 2026)
  5. QIAGEN. QuantiFERON-TB Gold Plus test result interpretation (manufacturer's interpretation table). qiagen.com (accessed November 10, 2026)
  6. Quest Diagnostics. QuantiFERON TB Gold Plus: frequently asked questions (FAQ204). questdiagnostics.com (accessed November 10, 2026)
  7. University of Iowa Health Care, Department of Pathology. Laboratory Services Handbook: QuantiFERON TB Gold. healthcare.uiowa.edu (accessed November 10, 2026)
  8. Children's Minnesota Laboratory. QuantiFERON-TB Gold Plus (test information sheet). childrensmn.org (accessed November 10, 2026)
  9. Pai M, Denkinger CM, Kik SV, et al. Gamma interferon release assays for detection of Mycobacterium tuberculosis infection. Clin Microbiol Rev. 2014;27(1):3-20. doi:10.1128/CMR.00034-13 (accessed November 10, 2026)
  10. Uzorka JW, Bossink AWJ, Franken WPJ, et al. Borderline QuantiFERON results and the distinction between specific responses and test variability. Tuberculosis (Edinb). 2018;111:102-108. doi:10.1016/j.tube.2018.06.002 (accessed November 10, 2026)
  11. Centers for Disease Control and Prevention. Clinical Overview of Latent Tuberculosis Infection. cdc.gov (accessed November 10, 2026)
  12. Centers for Disease Control and Prevention. Signs and Symptoms of Tuberculosis. cdc.gov (accessed November 10, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your result with your exposure history, symptoms, examination and chest X-ray.