The Tuberculin Skin Test (TST), often called the Mantoux test, screens for exposure to the bacteria that causes tuberculosis. This involves an intradermal injection of a small amount of purified protein derivative (PPD) solution, usually into the inner forearm, to check for an immune reaction. Proper care of the injection site immediately following administration is important for accurate results. Many people are concerned about managing daily activities, such as choosing appropriate clothing, without compromising the test.
Immediate Answer: Clothing and the Injection Site
Yes, wearing long sleeves after a TST is generally acceptable. The test involves a shallow injection just beneath the top layer of skin, creating a small, pale bump called a wheal. Standard, non-constricting clothing will not interfere with the reaction. Light contact from a shirt sleeve is not a concern for the test’s integrity; the goal is to avoid heavy pressure or constant friction on the injection site.
The test site is located on the inner surface of the forearm, typically two to four inches below the elbow joint. Covering the area with a loose sleeve is fine and can help protect it from accidental bumps. The wheal created by the injection normally disappears within 10 to 15 minutes as the fluid is absorbed.
Critical Care: What to Avoid for Accurate Results
While normal clothing is acceptable, specific actions must be avoided to ensure the test remains valid. The primary restriction is preventing friction or trauma to the area, which could cause a false-positive result or mask a true one. Do not scratch, rub, or aggressively towel-dry the injection site, even if it becomes mildly itchy. If the site feels itchy, applying a cold cloth or an ice cube wrapped in fabric can provide relief without damaging the test.
The site should not be covered with any type of bandage or adhesive dressing, as the tape may cause an allergic reaction mistaken for a positive result. Avoid applying creams, lotions, ointments, or antiseptic wipes to the area. These topical products may interfere with the skin’s ability to react. Although brief exposure to water is usually acceptable, the site should not be soaked in a bath or while swimming.
The Follow-Up: When and How the Test is Read
The TST must be read by a trained healthcare provider within a specific window of time to be considered valid. This mandatory window is between 48 and 72 hours following the initial injection. If the patient does not return within this three-day period, the test is considered invalid and must be repeated.
The reading measures the diameter of induration, which is the hard, dense, raised swelling that forms at the injection site. The provider uses a standardized technique of inspecting the arm and gently palpating the area to find the margins of the raised spot. Redness (erythema) is not measured; only the palpable hardening indicates a delayed-type hypersensitivity reaction. The measurement of induration is recorded in millimeters and is the sole factor used to determine the test’s outcome.