test bump larger than 5 mm, test result in the positive range.test bump smaller than 5 millimeters (mm), test result negative.The main consideration is the size of the bump on the arm: To do this, a doctor will measure the diameter of the wheal on the forearm and ask questions about the individual’s medical history and their environment.Ī doctor will need to consider several things when interpreting the results of a TB test. If a person does not attend this appointment, they will have to start the process over again.ĭuring the second appointment, a doctor will look to see how the body has responded to the injected tuberculin. The second stage of diagnosis must take place between 48-72 hours after the tuberculin injection.Īt this appointment, the doctor will check to see what has happened to the wheal on the skin.
Normal negative tb test pictures skin#
When it is done correctly, the injection will create a small, pale-colored bump on the skin called a wheal. The injection is usually done on the inside of the forearm. If an individual is infected with TB, their immune system will react to the tuberculin given in the TB skin test. Tuberculin is a fraction of purified protein derived from Mycobacterium tuberculosis. In the first, a doctor will inject someone with a small amount of a sterile solution, containing tuberculin.
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The skin test for TB, otherwise known as a Mantoux tuberculin test, can seem a bit intimidating, but it is quite straightforward. Image credit: Greg Knobloch, Centers for Disease Control and Prevention’s Public Health Image Library, 2004 Share on Pinterest The first part of the TB skin test will be an injection into the forearm with a small amount of tuberculin.