Other Ways to Determine a Food Allergy

Food Allergy Diagnosis: Blood Test

If you are extremely allergic and have severe anaphylactic reactions, your healthcare provider cannot use skin testing to make a food allergy diagnosis because causing an allergic reaction could be dangerous. Skin testing also cannot be done if you have eczema over a large portion of your body.
In those cases, a healthcare provider may use blood tests such as the RAST (radioallergosorbent test) or the ELISA (enzyme-linked immunosorbent assay) to make a food allergy diagnosis. These tests measure the presence of food-specific IgE in your blood. As with skin testing, positive tests do not necessarily mean you have a food allergy.

Food Allergy Diagnosis: Double-Blind Food Challenge

The final method healthcare providers use to diagnose food allergy is a double-blind food challenge. This testing has come to be the "gold standard" of allergy testing. In a double-blind food challenge:
  • Your healthcare provider will give you individual opaque capsules containing various foods, some of which are suspected of starting an allergic reaction.
  • You swallow a capsule and are watched to see if a reaction occurs. This process is repeated until you have swallowed all the capsules. In a true double-blind test, your healthcare provider is also "blinded" (the capsules having been made up by another medical professional). In that case, your provider does not know which capsule contains the allergen. The advantage of such a challenge is that if you react only to suspected foods and not to other foods tested, it confirms the food allergy diagnosis. You cannot be tested this way if you have a history of severe allergic reactions. In addition, this testing is difficult because it takes a lot of time to perform, and many food allergies are difficult to evaluate with this procedure. Consequently, healthcare providers seldom do double-blind food challenges.
This type of food allergy testing is most commonly used if your healthcare provider thinks the reaction you describe is not due to a specific food and wishes to obtain evidence to support this. If your healthcare provider finds that your reaction is not due to a specific food, then additional efforts may be used to find the real cause of the reaction.
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