Reaction to TB Test
Tuberculosis, or TB, is a bacterial infection commonly originating in the lungs. There are several different tests available to determine the presence or absence of TB. Each is associated with a specific reaction or symptom that allows a doctor to know whether or not an individual is TB positive or TB negative.
-
Time Frame
-
Reactions to a TB test surface at different times based on which test is administered. An X-ray or a blood test can usually determine a positive or negative internal reaction to TB in the shortest amount of time. A skin test will usually show results in 48-72 hours. However, a person will not usually exhibit a positive reaction to a skin test until 6 weeks after his first exposure to infection.
Skin Test Reaction
-
A TB skin test, also known as a Mantoux test, is the most common way of determining whether or not an individual has TB. It is performed by injecting a small amount of a substance known as PPD tuberculin underneath the skin. If a reaction occurs, it will do so in the form of a raised and thickened portion of the skin where the injection was delivered. This is known as induration. The exact size and extent of induration is the primary factor in determining the presence of TB.
A healthy individual with a normal immune system is considered TB positive if the size of induration exceeds 15mm. An individual is also considered TB positive if he has a smaller induration (5 to10mm) coupled with a chronic disease such as diabetes or rheumatoid arthritis. The presence of blisters around the injection site is also indicative of TB.
An individual is considered TB negative if he has an induration of less than 2mm without blistering.
-
Allergic Reactions
-
It is possible to develop a severe allergic reaction from the PPD tuberculin injection. This results in abnormal swelling and pain at the injection site. An allergic reaction may also culminate in a sore on the skin. Speak with a doctor if you develop such a reaction, as an alternative TB test may need to be given.
False Reaction
-
Often a person will not have a reaction to a TB skin test. Optimally, this will indicate a negative reaction to TB. However, this does not necessarily negate the presence of TB. Skin tests are not 100% accurate. A doctor will often schedule a blood test to provide further insight into whether or not an individual is infected, especially if the individual has recently been exposed to the TB bacteria.
A skin test can also cause a reaction such as puffy skin when there is no infection present or if a bacterium similar to TB is infecting the body. This is known as a false positive.
Warning
-
Speak with a doctor if you believe you have been exposed to TB and are in need of testing.
-
