Mythbuster: Is it true that the higher the result of the skin prick test, the more allergic you are?

Mythbuster: Is it true that the higher the result of the skin prick test, the more allergic you are?

People often assume that a large skin reaction in response to a skin prick test (also called a scratch test) or a high numerical value of the sIgE (specific IgE) blood test (referred to in the past as a RAST) means that an individual is more allergic to the substance than if the reaction and score are smaller.

This is not necessarily true. While the skin prick test checks for immediate allergic reactions, and the blood test looks for specific IgE to a given food or other substance to diagnose allergy, the results alone don’t necessarily correlate with the severity of a reaction to a given allergen. For example, the result of a small red bump (or wheal) to a skin prick test for peanut doesn’t necessarily imply that an allergic reaction will be mild.

Moreover, skin and blood tests carry some degree of risk of false positives or negatives. Your allergist will work with you to confirm or rule out an allergy, based on test results and a clinical history of the symptoms. Ask your allergist what your test results mean, and what foods you should avoid.

Medical content reviewed by: Dr. Julia Upton, MD, FRCP(C) Clinical Immunology and Allergy

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