TB Skin Test- 2 step tb test
2 step PPD SKIN TEST
The Mantoux tuberculin skin test (TST) is the standard method of determining whether a person is infected with Mycobacterium tuberculosis. Reliable administration and reading of the TST requires standardization of procedures, training, supervision, and practice.
How i s the TST Administered?
The TST is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) into the inner surface of the forearm. The injection should be made with a tuberculin syringe, with the needle bevel facing upward. The TST is an intradermal injection. When placed correctly, the injection should produce a pale elevation of the skin (a wheal) 6 to 10 mm in diameter.
How i s the TST Read?
The skin test reaction should be read between 48 and 72 hours after administration.
A positive result will form a red and swollen circle at the site of the injection. The size (diameter) of the swollen raised circle determines whether exposure to TB has occurred. The size that is considered positive varies with the health status and age of the individual. Even when infected, children, the elderly, and people who are severely immune compromised (such as those with AIDS) may have smaller, delayed, or even negative reactions to the TST.
wo-step testing with the Mantoux tuberculin skin test (TST) should be used for baseline or initial testing. Some people with latent TB infection have a negative reaction when tested years after being infected. The first TST may stimulate or boost a reaction. Positive reactions to subsequent TSTs could be misinterpreted as a recent infection.
What is a 2 step TB Test
Administer first TST following proper protocol
Positive — consider TB infected, no second TST needed; evaluate for TB disease.
Negative — a second TST is needed. Retest in 1–3 weeks after first TST result is read.
Administer second TST 1-3 weeks after first test
Positive — consider TB infected and evaluate for TB disease.
Negative — consider person not infected.
Is there anything else I should know?
Positive TST results are commonly seen in those who have received a BCG (Bacille Calmette-Guérin) vaccination. IGRA results are not affected by BCG.
A negative TST may cause mild itching or discomfort at the injection site. A person may not respond to a TB skin test (even with TB exposure) if the person has had a recent viral infection, a "live" vaccine (such as measles, mumps, chickenpox, influenza), or has overwhelming tuberculosis, another bacterial infection, or is taking immune suppressive drugs such as corticosteroids.
A person should generally wait 4-6 weeks to do a TB skin test after having had a vaccination with a live-virus vaccine.
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TB Skin Test Clinic Locations