The TST interpretation depends on the measured diameter of the induration and the clinical status of the patient.
- An induration of 15 or more millimeters is considered positive in all persons.
- An induration of 10 or more millimeters is considered positive in patients in the high-risk progression groups and in mycobacteriology laboratory workers.
- An induration of 5 or more millimeters is considered positive in the high-risk infection groups.