Interpretation of Tuberculin Skin Test Results and Cut-points in Various Risk Groups

TST result

Situation in which reaction is considered positive*

0-4 mm

  • In general this is considered negative, and no treatment is indicated
  • Child under 5 years of age and high risk of TB infection

≥ 5 mm

  • HIV infection
  • Contact with infectious TB case within the past 2 years
  • Presence of fibronodular disease on chest x-ray (healed TB, and not previously treated)
  • Organ transplantation (related to immune suppressant therapy)
  • TNF alpha inhibitors
  • Other immunosuppressive drugs, e.g., corticosteroids (equivalent  of ≥15 mg/day of prednisone for 1 month or more; risk of TB disease increases with higher doses and longer duration)
  • End-stage renal disease

≥ 10 mm

All others, including the following specific situations:

  • TST conversion (within 2 years)
  • Diabetes, malnutrition (<90% ideal body weight), cigarette smoking, daily alcohol consumption (>3 drinks per day)
  • Silicosis
  • Hematologic malignancies (leukemia, lymphoma) and certain carcinomas (e.g., head and neck)

*The goal of testing for LTB is to identify individuals who are at increased risk for the development of tuberculosis and therefore would benefit from treatment of LTB. Only those who would benefit from treatment should be tested so a decision to test presupposes a decision to treat if the test is positive.

Source: Canadian Tuberculosis Standards, 7th edition 2013, Chapter 4, Table 2 © All Rights Reserved. Canadian Tuberculosis Standards, 7th Edition. Public Health Agency of Canada 2013.