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Interpretation of TST reactions depends on the measurement (in millimeters) of the induration and the person’s risk of acquiring TB infection or the risk of progression to TB disease if infected.

5 or more millimeters

10 or more millimeters

15 or more millimeters

An induration of 5 or more millimeters is considered positive for

HIV-infected persons

Recent contacts of persons with infectious TB

People who have fibrotic changes on a chest radiograph

Patients with organ transplants and other immunosuppressed patients (including patients taking a prolonged course of oral or intravenous corticosteroids or TNF-a antagonists)

An induration of 10 or more millimeters is considered positive for

People who have come to the United States within the last 5 years from areas of the world where TB is common (for example, Asia, Africa, Eastern Europe, Russia, or Latin America)

Injection drug users

Mycobacteriology lab workers

People who live or work in high-risk congregate settings

People with certain medical conditions that place them at high risk for TB (silicosis, diabetes mellitus, severe kidney disease, certain types of cancer, and certain intestinal conditions)

Children younger than 5 years of age

Infants, children, and adolescents exposed to adults in high-risk categories

An induration of 15 or more millimeters is considered positive for

People with no known risk factors for TB