Tuberculin Test on Children

Tuberculosis Skin Test (also known as Tuberculin Test of PPD test) is a test used to determine if someone has developed an immune response to the bacterium that causes tuberculosis (TB). This response can occur if someone currently has TB, if they were exposed to it in the past, or if they received the BCG vaccine against TB.

It is administered by injecting a 0.1 mL volume containing 5 TU (tuberculin units) PPD into the top layers of skin (intradermally, immediately under the surface of the skin) of the forearm. The use of a skin area that is free of abnormalities and away from veins is recommended. The injection is typically made using a ¼- to ½-inch, 27-gauge needle and a tuberculin syringe. The tuberculin PPD is injected just beneath the surface of the skin. A discrete, pale elevation of the skin (a wheal) 6 to 10 mm in diameter should be produced when the injection is done correctly. This wheal or "bleb" is generally quickly absorbed. If it is recognized that the first test was improperly administered, another test can be given at once, selecting a site several centimeters away from the original injection.

"Reading" the skin test means detecting a raised, thickened local area of skin reaction, referred to as induration. Induration is the key item to detect, not redness or bruising. Skin tests should be read between 48 and 72 hours after the injection when the size of the induration is maximal. Tests read after 72 hours tend to underestimate the size of the induration.

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