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A skin prick test is much more accurate than the blood test.
Skin testing for food-specific immunoglobulin E (IgE) is used only in the diagnosis of IgE-mediated food allergies. Skin testing is more sensitive than in vitro testing (blood tests) in many cases. It should be performed by an allergy specialist because of both the risk of anaphylaxis and the skill required for proper interpretation. A positive skin test to a particular food only indicates the possibility that the patient has true allergy to that food. The specificity of skin testing for foods varies from 50 to 95 percent, depending upon the food in question and the patient's probability of having allergy. Further tests or food challenges are usually needed to confirm that the patient is truly reactive to the food upon ingestion. In contrast, a negative skin test result indicates the absence of an IgE-mediated allergy upon subsequent challenge with a 90 to 95 percent predictive accuracy. Further testing or challenge is sometimes indicated.