What Is The Difference Between A Skin Prick Test And A RAST Test?

— -- Question: What is the difference between a skin prick test and a RAST test?

Answer: The diagnosis of food allergy relates to finding IgE against that particular food. So your immune system has to have a reaction, or make an IgE, to a food, say, like peanuts. So there are two ways to look for IgE: one, by doing a skin prick test -- so that's putting the allergen on the forearm or the back and pricking it with something as simple as a sewing needle.

The other way would be to draw blood and take, in a serum, the clear part of the blood and looking for IgE. The old acronym for that is called a RAST test, which is a radioallergosorbent test. That's really equivalent to a Kleenex; a Kleenex is a brand name for a tissue. What we do now are not RAST studies, but they are studies to look for IgE by other means. So you can look for IgE by a skin prick test or you can look for it by the serum-specific test. Both give you excellent information and both should be fairly equivocal.

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