Determining if a Mantoux test is positive depends on the size of the induration (raised, hardened area) and the individual's risk factors.
A Mantoux test is considered positive based on the following induration size thresholds:
- ≥5 mm: Positive in individuals with certain risk factors.
- ≥10 mm: Positive in individuals with other risk factors or no known risk factors.
Here's a breakdown for clarity:
Interpretation of Mantoux Test Results
The size of the induration, measured in millimeters, is the main factor in interpreting the Mantoux test. However, the interpretation is further guided by the person's risk factors for tuberculosis (TB).
≥5 mm Induration is Considered Positive in:
- People with HIV
- People who have been in close contact with someone with infectious TB
- People with chest X-rays suggesting previous TB infection
- People who have had an organ transplant
- People who are immunosuppressed for other reasons (e.g., taking certain medications)
≥10 mm Induration is Considered Positive in:
- People who have come to the United States within the last five years from areas where TB is common
- People who inject illegal drugs
- People who live or work in high-risk congregate settings (e.g., prisons, nursing homes, homeless shelters)
- People with certain medical conditions that increase the risk of TB (e.g., diabetes, kidney disease, some cancers)
- Children younger than 4 years old
- Infants, children, and adolescents exposed to adults in high-risk categories
≥15 mm Induration is Considered Positive in:
- People with no known risk factors for TB
Important Considerations:
- A positive Mantoux test only indicates that the person has been infected with Mycobacterium tuberculosis. It does not mean they have active TB disease. Further testing, such as a chest X-ray and sputum samples, is needed to determine if active TB disease is present.
- Individuals who have received the BCG vaccine may have a positive Mantoux test. This can make interpretation more challenging.
- A negative Mantoux test does not completely rule out TB infection, especially in individuals who are immunocompromised.
In summary, without knowing the specific circumstances and risk factors of the individual being tested, it is impossible to definitively say whether a Mantoux test is positive. The induration size must be considered in relation to the person's medical history and risk factors for TB.
