How long tuberculosis test result

The preferred term for the test is tuberculin skin test, or TST. Includes guidance for administration, reading, and interpreting TSTs. Note: to remove the watermark on the document, click on the document's footer then click on the watermark text.

The skin test reaction should be read between 48 and 72 hours after administration. The reaction should be measured in millimeters of induration palpable, raised, hardened area or swelling. Do not measure erythema redness.

The indurated area should be measured across the forearm perpendicular to the long axis. Minus Related Pages. Reading the result of a TB skin test. To receive email updates about this page, enter your email address: Email Address.

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You will be subject to the destination website's privacy policy when you follow the link. Tuberculosis TB is an illness caused by a bacterial infection. This is called TB infection latent TB. This can affect any part of the body but usually affects the lungs. In Australia, both active and latent TB can be treated. It is a skin test to detect if you have been infected with TB bacteria.

A small amount of purified protein — taken from dead TB bacteria — is injected under the top layer of the skin, on the forearm. A small blister will appear at the site, which will disappear within 20 minutes. There may also be a small amount of blood at the needle site. A small lump may form at the injection site over the next few days and you will need to return to your doctor or nurse 3 days later to have this assessed. The size of your lump — measured in millimetres — will indicate whether or not you have a latent TB infection.

If the lump is below a certain size, the result of the test is negative. Usually this means that you have not been infected with TB bacteria. However, if your contact with TB was very recent, you may need to have the test repeated in 8 to 12 weeks. A false negative can occur if you are unwell, have a weak immune system, or have had a recent live vaccination.

If the lump is above a certain size, the result of the test is positive. It means that you may have been infected with the TB bacteria. It does not mean you have TB disease active TB. When you are infected with TB bacteria you are not infectious and you cannot pass the bacteria onto other people. You are not sick but, at some stage in the future, you may develop TB disease. If you are told your TST is positive you may be asked to see a doctor for review.

You will be given your result when you have the reading done.