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Tuberculosis Screening Test

A tuberculosis screening test checks if you have the bacteria that cause TB in your body. It can tell if you have been infected, but not whether the infection is active or inactive.

What this test measures

A tuberculosis screening test checks to see if you have the bacteria (germs) that cause tuberculosis (TB) in your body. TB is a bacterial infection that mainly attacks the lungs, but can also affect other parts of the body.

What your results mean

Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.

Higher-than-normal results

A positive result means that you have been infected with TB bacteria. You will need more tests to find out if you have an inactive TB infection or TB disease.

Lower-than-normal results

A negative result means that your skin or blood did not react to the test. You are unlikely to have an inactive TB infection or TB disease.

Frequently asked questions

What does a positive TB test mean?

A positive result means you have been infected with TB bacteria. You will need more tests, like a chest x-ray or sputum culture, to find out if you have inactive TB infection or active TB disease.

Can a TB test be wrong?

Yes. A false positive can happen if you've had the BCG vaccine or an infection from related bacteria. A false negative can happen if you were exposed within the past 8 to 10 weeks or had certain vaccines.

What is a borderline TB test result?

A borderline result means the test could not show for sure whether you have a TB infection. If this happens, you will likely be tested again.

What is the difference between a TB skin test and a TB blood test?

Both tests screen for TB infection. TB blood tests are more accurate than TB skin tests. Your provider can tell you which test is best for you.

Do I need more tests after a positive TB screening?

Yes. A positive screening test cannot tell if the infection is active or inactive. You will need additional tests such as a chest x-ray or sputum culture.

Related lab tests

Sources

Last updated . Information is aggregated from official public sources and is not a substitute for professional medical care.