Allergy Blood Testing – RAST

What is the RAST blood test for allergies?

While general blood tests give a picture of your overall health, specific allergy related blood tests can measure levels of immunoglobulin E (IgE), a key antibody that’s released during an allergic reaction.  While everyone’s body produces IgE, people who have allergies make larger quantities of this protective protein.

A blood test called RAST (radioallergosorbent) measures the levels of specific allergy related substances in your blood.

Blood testing for allergies is another good option particularly if:

• You cannot suspend antihistamine therapy which may inhibit skin tests;
• You are so sensitive to the allergen that the test might be risky;
• You have widespread skin disease making skin testing difficult; or
• If your skin cannot be skin tested for some other reason.

One problem with both blood and skin tests for food allergies is they are highly sensitive. So if you do have any remote or slight food allergy, the tests are likely to catch it. However, the tests are not specific enough. This means that the tests often are positive even when there is no significant food allergy.

Additionally, your physician may have you perform “use or elimination testing,” which is often used to check for food or drug allergies. Here, you will simply have to avoid certain items to see if you get better, or use suspected items to see if you feel worse.