What is the difference between RAST testing & Skin Prick Test? - Dr. Sreenivasa Murthy T M

RAST means Radio Allergo Sorbent Tests. The principle that is used is a radioimmunoassay wherein we try to evaluate a particular type of immunoglobulin and its level in the human blood for specific allergens. So RAST uses that principle by testing the blood of the human being suspected to have allergies to certain kind of allergens and see whether specific IgE’s are raised. Depending on the amount of IgE, which is raised, we will be able to come to a conclusion whether the person is allergic to it or not. A skin prick test, we utilize the same principle, but more as a demonstrative assessment of the patient by making small pricks in the skin and exposing the skin to known allergens and see how the body respond to that allergen and we compare it with the same skin, same injuries ,reaction to distilled water and compare it, so people who have an abnormal reaction to the allergens will show changes on the skin and show itching and we will be able to tell whether the person is allergic to it or not. Advantages of the skin prick test, it is an office based tests that can be done in the doctor’s office. It is immediate and within 20 minutes we will come to know if the person is allergic or not. Disadvantages are that it has to be done in the doctor’s office because in an occasional patient there will be allergic reaction and the doctor will have to manage with appropriate medication. Advantage of RAST, is that you just have to give a blood sample and you will get tested for a list of allergens and you will get the result after 4 or 5 days and you will be able to see the values and tell what you are allergic to. Advantage of RAST is that you continue to be allergic and you can repeat it at periodic intervals to see how your tires are and see whether you are continuously allergic or not and you want to be monitored when you are on a process called as immunotherapy for allergy. The flip side of RAST is that it is very expensive ,3 times more than that of a skin prick test. So what we prefer is a skin prick test in the doctor’s office and for this the people who are known to have certain skin allergies or people who show appropriate reactions to minor injuries called as dermographism on the skin in those people you prefer to get the RAST done.