How to Read Skin Test Results
Skin test results interpretation varies depending on the type of test. Let's break down how to read results for allergy and tuberculosis (TB) skin tests.
Allergy skin tests, such as prick tests, determine if you're allergic to specific substances. A positive result means an allergic reaction occurred. This is indicated by a raised wheal (a bump) at the test site.
- Positive Result: Indicates an allergy to the tested substance. The size of the wheal often correlates with the severity of the allergy; larger wheals typically indicate greater sensitivity. Results are often graded using a scale (e.g., +1 to +4) or descriptive terms (mild, moderate, strong). [Source: Decoding Allergy Skin Test Results: Reading the Chart, Mayo Clinic]
- Negative Result: Suggests no allergy to the tested substance. There's minimal or no reaction at the test site. [Source: Interpreting test results]
- Timing: Reactions are typically read 15-20 minutes after allergen application for prick tests, though this can vary. [Source: Reliability of skin test results when read at different time points]
Tuberculin Skin Tests (TST) for Tuberculosis
TSTs, like the Mantoux test, check for prior infection with Mycobacterium tuberculosis, the bacteria causing TB. The test involves injecting a small amount of tuberculin under the skin. The result is read by measuring the induration (hardened area) at the injection site, usually 48-72 hours after administration.
- Positive Result: A positive result indicates a possible TB infection. The size of the induration determines the interpretation, varying based on factors like risk factors and age. For example, an induration of 5mm or more might be positive in high-risk individuals, while 10mm or more might be positive in low-risk individuals. [Source: Clinical Testing Guidance for Tuberculosis: Tuberculin Skin Test, Administering, reading and interpreting a tuberculin skin test, TB test results and how to interpret]
- Negative Result: A negative result shows no evidence of TB infection.
- Important Note: A positive TST doesn't confirm active TB disease. Further tests are necessary to confirm diagnosis. Also, the BCG vaccine against TB can cause a false-positive reaction. [Source: Testing for Tuberculosis: Skin Test, Tuberculin Skin Test (TST)]
Remember: Always consult with a healthcare professional to interpret skin test results accurately. They will consider your medical history and other relevant factors for a proper diagnosis and treatment plan.
