Tuberculosis, also called TB, is a disease that is caused by the bacteria Mycobacterium tuberculosis. Though TB most commonly affects the lungs, it can infect other parts of the body. The most common symptom of TB is a severe painful cough that produces blood or sputum. TB can be fatal if left untreated. Skin testing can be performed with a healthcare provider to determine if an infection is present or if additional testing is needed to confirm or rule out tuberculosis.
Reading the TB Skin Test
Step 1
In a well lit environment, inspect the site where the test tuberculin was injected. Look for any skin that is reddened or appears to be elevated.
Step 2
Use fingertips to touch the area where the test was administered. Feel for any areas that are elevated from the surrounding skin and approximate the size of any elevation. This elevation is called induration.
Step 3
Use a washable marker to circle the area of induration. Do not include areas of redness, only circle skin that is elevated.
Step 4
Use the millimeter ruler to measure the size of the induration and record it on a piece of paper.
Step 5
Interpret your results using the following basic guidelines. A measurement less than 5 mm is generally considered to be a negative TB skin test. A measurement greater or equal to 5 mm is considered positive in certain patients, like those that are HIV positive or immunocompromised. A measurement greater than or equal to 10 mm is considered positive in high risk persons for TB exposure. A measurement greater than 15 mm is a positive result in someone with no risk factors for TB infection and no history of exposure.
Things You'll Need
- Trained healthcare worker
- TB skin test with tuberculin injected 48 to 72 hours prior to reading
- Millimeter ruler
- Good lighting
- Washable marker
