Reading a Mantoux test, also known as a tuberculin skin test (TST), involves checking for induration (a raised, hard area) at the injection site 48 to 72 hours after the injection. The size of the induration, not redness, determines the result.
Essential Steps for Reading a Mantoux Test
Here's a breakdown of the process:
- Timing is Key: The test must be read within 48 to 72 hours after the injection. Reading it outside this window can lead to inaccurate results.
- Prepare Your Fingers:
- Keep fingernails short: As noted in the provided information, your fingernails should be short enough so they do not extend beyond your fingertips. This prevents interfering with the accuracy of your palpation.
- Locate the Injection Site: Identify the precise area where the tuberculin was injected.
- Palpate the Area:
- Gentle Touch: Use the pads of your fingertips to lightly touch and sweep the area.
- Two-Inch Sweep: Lightly sweep your fingertips in a 2-inch area to identify the edges of any induration.
- Feel for Hardness: You are feeling for induration, which is a raised, hardened area under the skin. Redness alone is not indicative of a positive reaction and should be ignored.
- Measure the Induration:
- Use a Ruler: If induration is present, use a ruler to measure the diameter of the raised area in millimeters (mm). Do not measure the redness.
- Horizontal Measurement: Measure the diameter of the induration across the arm, horizontally.
- Document the Result:
- Record the measurement in millimeters.
- Note: If there is no induration, document that there is 0 mm of induration.
Interpreting Mantoux Test Results
Interpretation of the Mantoux test results depends on several factors, including:
- Size of Induration: The size of the induration (in millimeters) is the most important factor in determining whether the test result is positive, negative, or borderline.
- Risk Factors: The patient's medical history, potential exposure to tuberculosis, and other risk factors are also considered.
It is important to consult medical guidelines to understand how different induration sizes and patient risk factors are interpreted. Typically, a smaller measurement of induration might not be significant in a healthy adult, but might be concerning in someone with a compromised immune system.
Example Measurements
| Induration Size (mm) | Typical Interpretation (Context Dependent) |
|---|---|
| 0-4 mm | Negative reaction in most cases |
| 5-9 mm | May be considered positive in some at-risk populations |
| 10+ mm | Positive reaction in most individuals |
Key Points to Remember
- Palpation is Crucial: Rely on feeling the induration, as it may not always be visible.
- Redness Alone is Not a Result: Redness at the injection site should not be measured and does not count towards a positive result.
- Consult Medical Guidelines: Always refer to current medical recommendations to properly interpret TST results in the context of each specific patient.
- Professionals should always perform and read the test: The accurate reading of a Mantoux test, as per instructions, should be performed by a trained health professional.
By following these steps and understanding the importance of proper technique, you can accurately read and interpret a Mantoux test.
