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Several tests are used to diagnose tuberculosis (TB), depending on the type of TB suspected.
Your GP may refer you to a TB specialist for testing and treatment if they think you have TB.
Diagnosing pulmonary TB – TB that affects the lungs – can be difficult, and several tests are usually needed.
You may have a chest X-ray to look for changes in the appearance of your lungs that are suggestive of TB. Samples of phlegm will also often be taken and checked for the presence of TB bacteria.
These tests are important in helping to decide the most effective treatment for you.
Several tests can be used to confirm a diagnosis of suspected extrapulmonary TB, which is TB that occurs outside the lungs.
These tests include:
You may also have a lumbar puncture, where a small sample of cerebrospinal fluid (CSF) is taken from the base of your spine. CSF is fluid that surrounds the brain.
The sample can be checked to see whether TB has infected your brain and spinal cord (central nervous system).
In some circumstances, you may need to have a test to check for latent TB – where you've been infected with TB bacteria, but don't have any symptoms.
For example, you may need to have a test if you've been in close contact with someone known to have active TB disease involving the lungs, or if you've recently spent time in a country where TB levels are high.
If you've just moved to the UK from a country where TB is common, you should be given information and advice about the need for testing. Your GP may suggest having a test when you register as a patient.
The Mantoux test is a widely used test for latent TB. It involves injecting a small amount of a substance called PPD tuberculin into the skin of your forearm. It's also called the tuberculin skin test (TST).
If you have a latent TB infection, your skin will be sensitive to PPD tuberculin and a small, hard red bump will develop at the site of the injection, usually within 48 to 72 hours of having the test.
If you have a very strong skin reaction, you may need a chest X-ray to confirm whether you have active TB disease.
If you don't have a latent infection, your skin won't react to the Mantoux test. However, as TB can take a long time to develop, you may need to be screened again at a later stage.
If you've had the BCG vaccination, you may have a mild skin reaction to the Mantoux test. This doesn't necessarily mean you have latent TB.
The interferon gamma release assay (IGRA) is a blood test for TB that's becoming more widely available.
The IGRA may be used to help diagnose latent TB: