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RAST Tests

RAST tests were performed on blood drawn 24 hours after a first ever anaphylactic reaction to chinese food, If the RAST test for a specific allergen is negative, does that mean that that food will be safe? Specifically peanuts,almonds, brazil nuts, pecans, shrimp, lobster and celery were negative, and hazel nuts were positive. (Not all tests are back yet.) Does that mean that I can carefully try those items?

Skin testing will also be done in several weeks. If the results are at odds with RAST, which do we believe?

I do have an allergist, but like to have a variety of opinions.


Thanks for asking about RAST allergy testing.

The RAST (RadioAllergoSorbent Test) is a useful allergy test which measures specific allergy antibody (IgE) in serum. It is a 'marking' type of immune test which does not measure function and can not tell a physician exactly what will happen to a person with a positive test. The RAST is a measure of risk, much like a high cholesterol test indicates a high risk for the development of coronary heart disease. A positive test in the RAST indicates that you have a high risk of experiencing an allergic reaction (degree of reaction unknown) in the future.

Allergy skin testing is a 'functional' allergy test which actually shows you what can happen inside of the body when exposed to the specific allergen being tested. I often perform both the RAST and the skin testing in patients who have experienced a severe allergic reaction at a restaurant since many different food allergens may have been ingested, even if the food which caused the reaction was not ordered by the patient.

Negative skin tests and negative RAST tests are not predictive of future events, and do not tell you anything about the risks of experiencing another reaction.

All positive allergy tests need to be taken seriously if you have had a severe allergic reaction.

I hope that this information is useful to you.
Good luck.

Steve Kagen, M.D.