Tuberculosis (TB) Test
A tuberculosis (TB) test checks whether TB germs are in your body, using a skin test or a blood test. A positive result is followed by a chest X-ray and sputum tests to look for active disease.
What is a TB test?
A TB test is a skin or blood test that shows whether your immune system has met the germ that causes tuberculosis. It finds TB infection, but on its own it cannot tell inactive TB from active TB disease. Two tests are used in the US: the tuberculin skin test and the TB blood test, called an IGRA1. A positive result on either one leads to more tests1. Neither test looks for the germs themselves, because each reads how your immune system reacts to TB proteins. In the skin test, T cells cause a slow reaction under the skin2. In the blood test, white blood cells release a signal called interferon-gamma4. A negative result makes TB infection unlikely, yet more testing follows when there are symptoms, HIV or a recent exposure1.
Your TB test results tell you which of these next steps you need. The guide to TB test results explains each outcome.
What are the types of TB tests?
Two tests find TB infection, the skin test and the blood test, and two more look for TB disease. A chest X-ray and a sputum test are used only after a positive skin or blood test.
| Test | What it finds | When it is used |
|---|---|---|
| Tuberculin skin test (TST) | An immune reaction that signals TB infection | Screening people at higher risk1 |
| TB blood test (IGRA: QuantiFERON-TB Gold Plus or T-SPOT.TB) | An immune reaction that signals TB infection | Screening, including after the BCG vaccine4 |
| Chest X-ray | Signs of TB disease in the lungs | After a positive skin or blood test1 |
| Sputum smear and culture | TB germs in mucus coughed up from the lungs | When TB disease must be checked or ruled out1 |
A sputum check uses at least three samples, coughed up 8 to 24 hours apart6. One of them is taken early in the morning6. Smear results should come back within 24 hours of collection6. A NAAT finds TB DNA within hours, while a culture needs a week or more and remains the gold standard6. The page on how a tuberculosis test works explains the science behind each one.
How is the TB skin test done?
The TB skin test, also called the PPD or Mantoux test, puts 0.1 mL of tuberculin under the forearm skin. You return 48 to 72 hours later so a trained health worker can measure any firm swelling.
- A health worker uses a small needle to place the tuberculin just under the skin, raising a pale bump2.
- Nothing goes on the arm until the reading8.
- At the reading, the health worker measures the firm swelling in millimeters and ignores redness2.
- If the reading is missed, a new test is needed2.
A bruise or redness at the spot is not the result, because only firm swelling is measured2. Two FDA-approved tuberculin products are sold in the US, Tubersol and Aplisol, as CDC listed in 2019. Patients must not record their own result8. The full guide to the PPD skin test covers each reading.
How is the TB blood test done?
The TB blood test, or IGRA, is done by drawing blood from your arm and sending it to a lab for testing. It needs one visit for a blood draw, and results can be ready within 24 hours. Two brands are approved in the US: QuantiFERON-TB Gold Plus and T-SPOT.TB4. QuantiFERON reports its result as positive, negative or indeterminate4. The BCG vaccine does not affect the blood test5. In the lab, the blood is mixed with two TB proteins, ESAT-6 and CFP-104. The test then measures the interferon-gamma that white blood cells release in response4. An indeterminate or otherwise unclear result gives no useful answer, and a repeat blood test or a skin test may help4. For the most used brand, see the page on the QuantiFERON tuberculosis blood test.
How long does a TB test take?
A skin test is read 48 to 72 hours after placement, and blood test results usually take 24 hours to several days. So the skin test means a return trip for the reading, while the blood test needs no second visit. A skin test not read within 72 hours has to be repeated2. A single skin test takes at least 2 calendar days (Hawaii Department of Health, 2025). A two-step skin test takes at least 9 calendar days. Quest Diagnostics lists QuantiFERON results in 2 to 3 business days. The page on how long QuantiFERON results take breaks the wait down.
Who should get a TB test?
You should get a TB test if you are more likely to have met TB germs or to get sick from them. People at low risk generally do not need one.
These groups have a higher chance of infection1:
- Born in, or often visiting, a country where TB is common
- Living or working in a shelter, prison, jail, hospital or nursing home
- Recent contact with someone who has active TB
- Health care workers
These groups have a higher chance of getting sick once infected1:
- A weak immune system, including HIV
- Infection in the last 2 years
- Young children and older adults
- People who inject drugs
After an exposure, a test 2 to 8 weeks later catches an infection the first test missed2. A contact whose blood test is negative is tested again 8 to 10 weeks after the last exposure4. If you spent time near someone who was sick, read what to do when exposed to tuberculosis.
Where can I get a TB test?
You can get a TB test through your own health care provider or your local health department. CDC guidance from 2024 advises contacting your state or local TB program to find a test near you. Public and private health plans may cover the cost of TB testing1. In 2024, CDC listed 51 state TB programs, covering the 50 states and DC, plus 8 city programs. The Philadelphia TB Control Program tests children and adults for free, with or without insurance. Local options are listed under where to get a tuberculosis test.
Should you get a skin test or a blood test for TB?
You should ask your provider which to get, since the skin test and the blood test for TB find the same infection. CDC guidance from 2025 prefers a blood test after BCG or if returning is hard, and a skin test under age 5. BCG can make a skin test falsely positive, but it does not affect the blood test5. The blood test is safe in pregnancy5. CDC noted in 2024 that the blood test may cost more than a skin test. In very young children, the amount of blood needed can be a practical barrier4. The comparison of a skin test or blood test for tuberculosis goes further.
What happens after a positive TB test?
A positive TB test means TB germs are in your body, not that you are sick or contagious. The next step is a chest X-ray and, often, a sputum test to check for active TB disease. A normal X-ray with no symptoms usually means inactive TB, which can be treated to prevent disease1. CDC pages from 2025 use the name inactive TB for latent TB infection. An abnormal chest X-ray cannot confirm TB disease on its own6. Without treatment, 1 in 10 people with inactive TB get sick with active TB disease7. Treatment is 90% effective at preventing that2. A positive result can stay positive for life, so keep a written record of it3. The page on a positive TB test explains the result in depth.
What else should you know about TB tests?
These short answers cover diagnosis, side effects, pain, preparation, aftercare, accuracy and work.
Can a TB test tell you if you have TB disease?
No, a TB test on its own cannot tell whether you have TB disease. Symptoms, a chest X-ray and sputum tests decide that. Signs include a cough lasting 3 weeks or more, as the page on how to know if you have tuberculosis explains.
Does a TB test have side effects?
Yes, mostly mild ones, such as itching, swelling or irritation where the skin test was placed. Any swelling days later is read by a health worker, because only firm swelling counts as the result. A correct skin test raises a pale bump 6 to 10 mm across, unlike a reaction to a tuberculosis skin test2.
Does a TB skin test hurt?
Yes, a little: a fine 27-gauge needle places the tuberculin just under the top layer of skin. The TB blood test, by contrast, is an ordinary draw of blood from a vein in the arm. The Tubersol label lists pain at the injection site, and the page on skin test placement shows how it is given.
Which disease does a TB test look for?
A TB test looks for tuberculosis, an infection caused by the bacterium Mycobacterium tuberculosis. The disease usually affects the lungs and spreads through the air. TB can reach the brain, kidneys or spine too, as the home page on tuberculosis explains.
Do you need to fast for a TB blood test?
No, a TB blood test needs no fasting or other special preparation before the blood draw. Quest Diagnostics lists no special preparation for its QuantiFERON-TB Gold Plus test. QuantiFERON uses four small tubes with 1 mL of blood in each, as the page on QuantiFERON blood draw tubes shows.
What should you avoid after a TB skin test?
You should avoid scratching, scrubbing, lotions and adhesive bandages on the test site until it is read. Keep the spot clean and dry, and leave the reading to a trained health worker. A cold compress may ease the area, and the page on an itchy tuberculosis (TB) skin test has more tips8.
How accurate is a TB test?
TB skin and blood tests detect most people with TB, and the blood tests give fewer false positives in healthy people. Neither test is perfect, so a result is weighed with risk factors, symptoms and a chest X-ray. A 2010 CDC review found 95% sensitivity for the skin test, so a negative tuberculosis test can still miss some infections9.
Do you need a TB test for work or school?
Yes, for health care jobs: CDC guidance from 2019 calls for a baseline TB test when a health care worker is hired. Workers who are tested again over time get a two-step skin test as their first, baseline test. After the baseline, CDC guidance from 2019 advises no routine yearly testing, as the page on a TB test for employment explains.
- CDC, Testing for Tuberculosis, June 17, 2024, https://www.cdc.gov/tb/testing/index.html.
- CDC, Clinical Testing Guidance for Tuberculosis: Tuberculin Skin Test, Jan. 31, 2025.
- CDC, Tuberculosis Skin Test, Jan. 31, 2025.
- CDC, Clinical Testing Guidance: Interferon Gamma Release Assay, May 9, 2024.
- CDC, TB Blood Test, Jan. 31, 2025.
- CDC, Clinical and Laboratory Diagnosis for Tuberculosis, Jan. 31, 2025.
- CDC, About Inactive Tuberculosis, Jan. 16, 2025.
- Minnesota Department of Health, Tuberculin Skin Test (TST), July 6, 2026.
- Mazurek et al., Updated Guidelines for Using IGRAs, CDC MMWR 59(RR-5), June 25, 2010.
Also cited by name: CDC, About Tuberculosis, Jan. 17, 2025; CDC, Signs and Symptoms of Tuberculosis, Jan. 17, 2025; CDC, MMWR 68(24), June 21, 2019; CDC, MMWR 68(19), May 17, 2019; CDC, TB Programs, Apr. 29, 2024; TUBERSOL label, DailyMed, May 1, 2026; Hawaii Department of Health, State TB Requirements, Dec. 1, 2025; City of Philadelphia, Get tested for tuberculosis; Quest Diagnostics, QuantiFERON-TB Gold Plus, read Nov. 1, 2026; QIAGEN, QFT-Plus product pages.
