Tuberculin skin test is indeed a type 4 hypersensitivity reaction. This test is used to diagnose tuberculosis by detecting the immune response to the bacteria that cause the disease. The test involves injecting a small amount of tuberculin, a purified protein derivative of the bacteria, under the skin and then observing the reaction after 48-72 hours. If the person has been exposed to the tuberculosis bacteria before, their immune system will mount a delayed hypersensitivity reaction. This reaction is characterized by the infiltration of immune cells, primarily T cells, into the site of injection, resulting in the formation of a raised, red bump known as an induration. This response is mediated by sensitized T cells that have been previously exposed to the tuberculosis bacteria and have become activated upon re-exposure. The tuberculin skin test is an important tool in the diagnosis of tuberculosis, but it is not without limitations. False positive results can occur in individuals who have been vaccinated with the bacillus Calmette-Guérin (BCG) vaccine or who have been exposed to non-tuberculosis mycobacteria. False negative results, on the other hand, may occur in individuals who are immunocompromised or who have been recently infected with the tuberculosis bacteria. Overall, the tuberculin skin test remains a valuable tool in the diagnosis of tuberculosis and the management of the disease.
What hypersensitivity reaction is a TB test?
[10] This local reaction indicates the presence of type four hypersensitivity. The tuberculin test is a validated method to diagnose tuberculosis infection, even if latent.
What does a failed TB test look like?
If you have an Mtb infection, the skin around the injection site should start to swell and harden within 48 to 72 hours . This bump, or induration, may also change color. But the induration’s size, not the color, will determine your results. An induration of less than 5 millimeters (mm) is a negative result.
What does an allergic reaction to a TB test look like?
Some people experience some redness, rash, slight bruising or a small bump at the site. DO not WORRY! These reactions are common and do not necessarily mean you have a positive test. On a rare occasion, some people are very sensitive to the solution and develop a severe skin reaction.
What does a positive TB tine test look like?
Tuberculosis. Within 48 to 72 hours, a positive TB skin test is marked by an area of reddish induration greater than 10 mm. It is the induration (firm bump) that is gently palpated that determines the size, not the area of redness. This reaction is slightly larger than the average positive test 17 mm in size.
