Classification of TB skin test reactions
An induration of 5 or more millimeters is considered positive in:
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People with HIV
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Recent contacts of people with infectious TB disease
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People with chest x-ray findings suggestive of previous TB disease
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People with organ transplants
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Other immunosuppressed people (e.g., patients on prolonged therapy with corticosteroids equivalent to/greater than 15 mg per day of prednisone or those taking TNF-α antagonists)
An induration of 10 or more millimeters is considered positive in:
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People born in countries where TB disease is common, including some countries in Asia, Africa, and Latin America
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People who misuse drugs and alcohol
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People who live or work in high-risk congregate settings (e.g. nursing homes, homeless shelters, or correctional facilities)
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Mycobacteriology laboratory workers
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People with certain medical conditions that place them at high risk for TB (e.g. silicosis, diabetes mellitus, severe kidney disease, certain types of cancer, or certain intestinal conditions)
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People with a low body weight (<90% of ideal body weight)
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Children younger than 5 years of age
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Infants, children, and adolescents exposed to adults in high-risk categories
An induration of 15 or more millimeters is considered positive in:
- People with no known risk factors for TB