A positive TB skin test is generally defined as an induration (a firm, raised area) of 10mm or larger in diameter.
However, the criteria for a positive TB skin test can vary based on individual risk factors. A smaller induration size of 5mm or larger is considered positive in certain high-risk groups.
Here's a breakdown:
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General Cutoff: 10mm or more is considered positive for most individuals.
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Higher-Risk Individuals: A reaction of 5mm or more is considered positive in:
- People with HIV
- People who have been recently exposed to someone with TB
- People with organ transplants
- People with other conditions that weaken the immune system.
- People who have fibrotic changes on prior chest X-rays consistent with prior TB disease.
It's essential to consult with a healthcare professional for proper interpretation of TB skin test results, as they can assess individual risk factors and provide appropriate guidance. Your healthcare provider will consider your health history, potential exposure to TB, and other risk factors to determine if your test result is positive.
