How Serious is an Allergic Reaction to a TB Skin Test?
Tuberculosis, an often fatal disease, is caused by Mycobacterium tuberculosis, a bacterium. The most common test for determining exposure is a skin test. For some, this test can cause an allergic reaction. The question then is just how serious is an allergic reaction to a TB skin test?
Tuberculosis (TB) usually affects the pulmonary system. It is transmitted through inhalation of minute droplets of sputum (as from a cough or sneeze). More rarely it can be caught by drinking infected milk (cows can carry bovine tuberculosis). It can affect any part of the body, though it most commonly affects the pulmonary system, though. The bacteria builds up, dies, and scar tissue forms around the infection sites without causing any more tissue damage in those whose immunity relieves them of the bacteria. In those whose natural immunity does not engage, the disease spreads and causes vacuoles in the lungs, leading to death over time.
The procedure for finding if a patient has ever been infected with tuberculosis or related bacteria is called a tuberculin test. It uses tuberculin, a preparation made from dead tuberculosis cells. A small amount is injected under the skin’s surface (usually on the inside of the forearm). A reddish swelling will occur usually within 24 hours if the reaction is considered “positive”. However, the test is only a starting point for confirmation of the presence of TB: the tell-tale swelling can occur in those who have also been immunized with BGC vaccine (common in parts of the world where TB is particularly rampant). A “false positive” reading can also occur in people who have been merely exposed to the bacteria. Furthermore, the test can only determine if such exposure has occurred, not when – a person may yield a false positive, for example, if he or she was in contact with someone carrying the disease in childhood, and years later the reaction will still be present. A “positive” reading does not necessarily mean the patient has tuberculosis, only that exposure has happened at some time in the patient’s life. Further blood work is required to complete the diagnosis. The best use of the tuberculin test is for exclusion — no reaction means there is no TB in the body.
As with any injection of foreign matter into the skin an allergic reaction to TB skin test can occur in some people. How serious is an allergic reaction to a TB skin test? That depends upon the person. The reddening associated with a mild, non-fatal allergic reaction’s tell-tale histamine build in the body may mimic a “false positive” reading, leading to a need for further testing to exclude tuberculosis. Some people’s allergic reactions to the tuberculin could result in anaphylaxis, the condition causing anaphylactic shock, coma, and death.
Thus, an allergic reaction to TB skin testing is nothing to ignore, regardless of how mild the initial symptoms may be. At the least, the patient may need further testing by different methods to confirm or exclude tuberculosis. Death is certainly a possibility in severe reactions. Consulting a physician before submitting to a TB skin test may help uncover an allergy problem before it is too late.