What is the difference between a skin prick test and a blood or RAST test?
The skin prick test or a blood test, such as the RAST (or radioallergosorbent test), is commonly used to begin to determine if an allergy exists. (The RAST is sometimes called the CAP-RAST or ImmunoCap test.) A skin prick test is usually cheaper and can be done in the doctor’s office. The doctor places a drop of the substance being tested on the patient’s forearm or back and pricks the skin with a needle, allowing a tiny amount to enter the skin. If the patient is allergic to the substance, a wheal (mosquito bite-like bump) will form at the site within about 15 minutes. A RAST test requires a blood sample. The sample is sent to a medical laboratory, where tests are done with specific foods to determine whether the patient has IgE antibodies to that food. The results are usually received within one week.
