Tuberculin Skin Test Interpretation for Tuberculosis Detection

Interpretation Criteria by Risk Group

• The American Thoracic Society recommends that an induration size of ≥5 mm is considered positive in high-risk individuals, such as HIV-positive individuals, recent contacts of TB cases, and persons with fibrotic changes on chest radiographs consistent with prior TB 1, 4, 6, 7
• The Centers for Disease Control and Prevention suggests that an induration size of ≥10 mm is considered positive in moderate-risk individuals, including recent arrivals from high-prevalence countries, injection drug users, and persons with clinical conditions that increase TB risk 1, 4, 7
• The American College of Chest Physicians recommends that an induration size of ≥15 mm is considered positive in low-risk individuals, such as those with no known risk factors for TB 1, 4, 8

Special Considerations

• A positive tuberculin skin test result in BCG-vaccinated persons should be considered indicative of TB infection, especially in persons from high-prevalence countries 2, 3
• Skin test conversion is defined as an increase in reaction size of ≥10 mm within 2 years, indicating recent infection 3, 6

Follow-up Evaluation

• The Centers for Disease Control and Prevention recommends that all persons with positive tuberculin skin test results should undergo further examination, typically starting with a chest radiograph 5, 7
• High-priority contacts should undergo further examination regardless of skin test results 5
• A negative test result obtained <8 weeks after exposure is considered unreliable for excluding infection, and follow-up testing at 8-10 weeks after exposure ends is recommended 5