What is the method of reading the tuberculosis skin test?
“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 48-72 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. How are skin test results interpreted? The basis of the reading of the skin test is the presence or absence and the amount of induration (localized swelling). The diameter of the induration should be measured transversely (for example, perpendicular) to the long axis of the forearm and recorded in millimeters. The area of induration (palpable, raised, hardened area) around the site of injection is the reaction to tuberculin. It is important to note that redness is not measured. A tuberculin reaction is classified as positive based on the diameter of the induration in conjunction with certain patient-specific risk factors. In a healthy
