> 5 mm Considered Positive for:
  • Human immunodeficiency virus (HIV)-positive persons
  • Recent contacts 1 of Tuberculosis (TB) case patients
  • Fibrotic changes on chest radiograph consistent with prior TB
  • Patients with organ transplants and other immunosuppressed patients (receiving the equivalent of > 15 mg/d of prednisone for 1 mo. or more)

> 10 mm considered positive for:

  • Recent immigrant (i.e. within the last 5 years) from high prevalence countries
  • Injecting drug users
  • Residents and employees 2 of the following high-risk congregate settings: prisons and jails, nursing homes and other long term care facilities for the elderly, hospitals and other health-care facilities, residential facilities for patients with acquired immunodeficiency syndrome (AIDS) and homeless shelters
  • Mycobacteria laboratory personnel
  • Persons with the following clinical conditions that place them at high risk: silicosis, diabetes mellitus, chronic renal failure, some hematologic disorders (e.g. leukemias and lymphomas) other specific malignancies (e.g., carcinoma of the head, or neck and lungs), weight loss of > 10% of ideal body weight, gastrectomy, jejunoileal bypass
  • Children younger than 4 years of age or infants, children and adolescents exposed to adults at high-risk

> 15 mm considered positive for:

  • Persons with no risk factors for TB

TST Conversion: An increase in reaction of >10 mm within 2 years should be considered a TST conversion indicative of recent infection with M.tb. infection.

1 Recent contacts are individuals who have shared air for a prolonged period of time with someone who has infectious M.tb (from hours to months depending on the circumstances).

2 For persons who are otherwise at low risk and are tested at the start of employment a reaction of >15 mm induration is considered positive.

Reference: American Thoracic Society, Centers for Disease Control. 2000. Targeted Tuberculin Testing and Treatment of Latent Tuberculosis Infection. American Journal of Respiratory Critical Care Medicine. Vol. 161, No. 4, Part 2.


This information is provided by Tuberculosis Prevention and Control Program within the Department of Public Health.