What it means
A test that shows whether a person's immune system has met the bacterium that causes tuberculosistoo-ber-kyoo-LOH-sisAn infection caused by the bacterium Mycobacterium tuberculosis, which most often attacks the lungs.tubercul/o small swelling-osis abnormal conditionFull entry . A tiny amount of purified tuberculin protein is injected into the top layers of the skin (intradermal), and the site is read 48 to 72 hours later. The reader measures the firm, raised area (induration) in millimeters, not the redness. Whether a result counts as positive depends on the person's risk: 5 mm or more for people with HIV, a weak immune system or close contact with an active case; 10 mm or more for groups such as health care workers and recent arrivals from high-risk countries; 15 mm or more for people with no risk factors.
For the nurse
Inject intradermally so a small bleb forms, do not rub or cover the site, and make sure the client comes back within 48 to 72 hours for the reading. A positive test means infection at some point, not active disease: a chest x-rayEKS-rayA picture of the inside of the body made with a small dose of radiation; also called a radiograph.Full entry and assessment follow. People who had the BCG vaccine can test positive, so a blood test (interferon-gamma release assay) may be used instead.
In a chart
"TST read at 48 hours: 12 mm induration left forearm; provider notified, chest x-ray ordered."
At a glance
| Spanish | prueba cutánea de la tuberculina |
|---|---|
| Also written | purified protein derivative, TST, tuberculin skin tests |
Related terms
tuberculosis
An infection caused by the bacterium Mycobacterium tuberculosis, which most often attacks the lungs.
pulmonary tuberculosis
Tuberculosis of the lungs, caused by the bacterium Mycobacterium tuberculosis.