A normal Mantoux test result shows an induration (hardened area) of less than 5 mm. However, the interpretation depends on several factors, including the individual's risk factors for tuberculosis (TB) and the context of the test.
Understanding Mantoux Test Results
The Mantoux test, also known as the tuberculin skin test, measures your body's immune response to tuberculosis bacteria. The test involves injecting a small amount of purified protein derivative (PPD) under the skin. After 48-72 hours, a healthcare professional measures the size of any induration that develops.
The reference ranges provided in various sources indicate:
- Less than 5 mm: Generally considered negative, indicating no significant exposure to TB bacteria.
- 5-15 mm: Interpreted based on risk factors. A positive result in high-risk individuals (e.g., recent contact with a TB patient, immunosuppression) would indicate further investigation. In low-risk individuals, it might warrant further testing.
- More than 15 mm: Generally considered positive, suggesting a possible TB infection. However, additional testing is always necessary to confirm active TB disease.
Important Considerations:
- Individual Risk Factors: Interpreting the test results requires considering the individual's risk factors for TB. A 10mm induration in a low-risk individual might be considered negative, while the same size in a high-risk individual may suggest further evaluation.
- Accuracy Limitations: The Mantoux test isn't perfect. A false-positive result can occur due to previous BCG vaccination or exposure to non-tuberculous mycobacteria. Conversely, a false-negative result can happen if the immune system is weakened.
- Additional Testing: A positive Mantoux test doesn't automatically diagnose active TB. Further testing, such as chest x-rays and sputum cultures, is essential to confirm the diagnosis.
The size of the induration is not the sole determining factor for a Mantoux test interpretation; other clinical factors must be taken into consideration by a healthcare professional. This information should not be used for self-diagnosis or treatment. Consult a healthcare professional for any concerns regarding the Mantoux test.
