The Tuberculin Skin Test (TST), also known as a Mantoux test, is used to assess whether a person has been infected with the tuberculosis (TB) bacteria.
The TST is primarily used to diagnose TB infection. This is when the TB bacteria is in the body but the person is not experiencing any symptoms suggestive of TB disease.
The TST (or Mantoux test) indicates whether a person has been infected with Mycobacterium tuberculosis (the bacteria causing TB) by measuring if the body’s immune response to TB has been stimulated. A TST may be used to diagnose latent TB infection. It is not used to test for TB disease.
A TST involves a small injection of tuberculin (or purified protein derivative – PPD) into the skin, usually on the forearm. After 48-72 hours the injection site is assessed for any reaction (lump). If a lump develops it will disappear within days without any treatment.
Latent TB infection is when a person has the TB bacteria in their body but the immune system is stopping the infection from causing disease. Latent TB infection causes no symptoms and cannot be passed on to other people.
There is a small risk that latent TB infection can progress to TB disease. The risk is increased in young children and old people, as well as people with weak immune systems. TB disease develops if the TB bacteria start to multiply and cause symptoms, such as a fever, unexpected weight loss, tiredness or a cough that won’t go away. Latent TB infection can be treated with special antibiotics to prevent it from progressing to TB disease in the future.
The interferon gamma release assay (IGRA) is another test for latent TB infection. It is a blood test and also measures the body’s immune response to TB bacteria.
Your nurse or doctor will explain the advantages and disadvantages of the different tests and advise which is more suitable for your situation. In some situations both TST and IGRA testing may be required.
It is important to let the nurse or doctor know if you:
These conditions may affect the test result.
After the TST you must return to the clinic 48-72 hours later so that any reaction can be assessed and recorded. Some people who have a negative TST may need a second TST, while some people with a positive TST may require an IGRA (blood test). Your nurse or doctor will explain why further tests may be needed.
Contact your local TB service for more information