A positive TB skin test appears as a firm, red bump at the injection site. The healthcare provider will measure the size of this raised area (induration) to determine the result. A larger bump generally indicates a positive result. It's important to note that the size of the bump, along with other risk factors, is considered when interpreting the test. A negative test will show little to no reaction.
Understanding the TB Skin Test Result
- Positive Result: A firm, red bump (induration) of a certain size or larger (the size varies depending on guidelines and individual risk factors). One reference cites a positive result if the swelling's diameter is greater than 15 mm.[1] The appearance may also include redness and sometimes even a rash or itching at the site, though these are not solely indicative of a positive test.[2, 3]
- Negative Result: Little to no reaction at the injection site; essentially, the absence of a noticeable bump.[4]
Important Considerations
- Individual Risk Factors: The interpretation of the TB skin test result is not solely based on the size of the bump. The healthcare provider will consider your individual risk factors when assessing the results.[5, 6]
- Further Testing: A positive TB skin test does not automatically mean you have active tuberculosis. Further testing is typically required to confirm a diagnosis.[7]
- Professional Interpretation: It is crucial to have the test evaluated by a healthcare professional, as self-interpretation can be misleading.
[1] Healthline, "What Does a Positive TB Test Look Like?", Oct 25, 2022
[2] Westford, MA, "Tuberculosis (TB) Skin Testing (Mantoux/PPD)", Accessed [date]
[3] Minnesota Department of Health, "The TB Skin Test (Mantoux)", Nov 14, 2022
[4] Quora, "What does a negative TB skin test look like?", Dec 7, 2015
[5] Cleveland Clinic, "TB (Tuberculosis) Test: Purpose, Procedure & Results", Apr 15, 2022
[6] HealthLink BC, "Tuberculin Skin Test", Feb 26, 2024
[7] Mount Sinai, "PPD skin test Information", Accessed [date]
