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Tuberculosis Screening
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Tuberculosis Screening

Tuberculosis (TB) screening tests determine if you have been infected with the bacteria that cause TB, a serious infection that primarily affects the lungs.

What is a tuberculosis (TB) screening test?

TB screening checks for the bacteria that cause tuberculosis. There are two types of TB conditions:

  • Inactive (latent) TB: You have the germs in your body, but they are not active. You do not have symptoms and cannot spread the disease, but treatment is often recommended to prevent future illness.
  • Active TB disease: The germs are actively growing and making you sick. This condition is contagious and requires antibiotic treatment.

The two primary screening methods are the TB skin test (Mantoux test) and the TB blood test (IGRA test).

Why do I need a TB screening test?

You may need screening if you have been exposed to someone with active TB, are starting a new job or school, or are at high risk. High-risk factors include:

  • Working in healthcare, jails, nursing homes, or shelters.
  • Frequent travel to countries where TB is common.
  • Having a weakened immune system, such as from HIV, diabetes, or treatments for conditions like rheumatoid arthritis or Crohn's disease.

What happens during a TB screening test?

  • TB Skin Test: A professional injects a small amount of fluid (tuberculin) under the skin of your arm. You must return after two to three days to have the site checked for a reaction.
  • TB Blood Test: A professional collects a blood sample from a vein in your arm.

What do the results mean?

  • Positive: You have been infected with TB bacteria. Further tests, such as a chest x-ray or sputum culture, are required to determine if the infection is active or inactive. False positives can occur if you have received the BCG vaccine.
  • Negative: You are unlikely to have a TB infection. However, you may still need further testing if you have symptoms or were tested too soon after exposure.
  • Borderline (Indeterminate): The test could not confirm an infection, and you will likely need to be retested.

While both tests are accurate, TB blood tests are generally considered more accurate than skin tests.

Frequently Asked Questions

It’s best to wait 8‑10 weeks after a known exposure before testing, because the immune response may not be detectable earlier. Testing sooner can yield a false‑negative result; if you need an earlier test (e.g., for a job), repeat the test after the 8‑week window.
The skin test (Mantoux) measures a delayed‑type skin reaction, while the interferon‑gamma release assay (IGRA) measures immune response in a blood sample. IGRA is not affected by prior BCG vaccination, so it is preferred for people who received BCG or who may have difficulty returning for the reading.
Yes. Immunosuppressive conditions (HIV infection, solid‑organ transplant, chemotherapy, corticosteroid use > 15 mg/day for > 1 month) can blunt the immune response and produce false‑negative skin or blood tests. Recent viral infections, very young age (< 2 years), or severe malnutrition can also reduce test sensitivity.
positive screening test prompts a chest X‑ray to look for radiographic signs of active TB. If the X‑ray is abnormal or if you have symptoms (cough, fever, night sweats, weight loss), sputum samples for acid‑fast bacilli smear and culture are obtained. If the X‑ray is normal and you have no symptoms, you are likely to have latent TB and will be evaluated for preventive therapy.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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