Food Allergy Resources

What is a RAST Test ? What is a CAP-RAST Test?

January 2007

What is a RAST test?

A RAST (RadioAllergoSorbent Test) is a blood test done to look for allergies. This is a way to look for Immunoglobulin E (IgE), the allergic antibody. IgE is a protein in our body that attaches to food proteins to start an allergic reaction. In order to have an allergic reaction, you need to have IgE to the food in question. A RAST test looks for IgE in your blood. This test can’t tell you if you will react or how severely you will react, but tells you that you have IgE against the food.

What is a CAP-RAST test?

A CAP-FEIA (or Immunocap) RAST test is a specific type of RAST (see above). It is also a blood test. Immunocap is a brand name of a type of RAST test. This is the brand that was used in many of the research studies of food allergies. This test is different from generic RAST tests because it allows your doctor to measure exactly how much IgE is present to a specific food or allergen. It is more exact than a generic RAST. The information from this test, in addition to the skin prick test (SPT), is helpful to an allergist because it can be compared to known values and determine the chance you will have an allergic reaction to a food. This test CANNOT tell you how severe an allergic reaction will be if you accidentally eat a food to which you are allergic.

Is there a difference between a RAST and CAP-RAST?

Yes. A CAP-RAST or Immunocap is a brand or type of RAST. It is more specific and can be compared to charts to help determine if you or your child is at risk of an allergic reaction to a food. It is up to your doctor to decide which test is right for you and which test will provide the most information for your care.

Approved by Medical Advisory Team January 2007