A positive TB, or tuberculin, test appears red and raised at the test puncture site, according to WebMD. For high-risk patients, a small red bump at the site of puncture is considered positive, and for a low-risk patient, a larger red bump is considered positive.
High-risk patients are patients who are immunosuppressed or who have been in contact with patients who have active TB, states WebMD. These patients have a lesser reaction to a TB test and may need a chest X-ray to determine if they have TB. Low-risk patients are on the opposite end of the spectrum and have never been exposed to TB. Their reactions are greater.