To identify the allergen(s) triggering your symptoms, either a skin test (scratch test or patch test) or a simple blood test (called the serum allergy test) may be done. The differences between these types of tests are listed below.
An allergy skin test is done by an allergy specialist (allergist) and involves exposing your skin to a variety of suspected allergens, like pollen, mold, animal dander, dust mites and food, to observe whether a reaction occurs. A skin test can either be a scratch test or a patch test. With both types of tests, if a positive reaction occurs, like swelling or itching, you may have an allergy to that substance.
For the scratch test, small droplets of allergy-causing substances are placed on your skin and then the outer-layer of your skin is lightly scratched to allow the allergen to enter. The allergist will then have you wait for 15-20 minutes to monitor for a skin reaction to the substance(s) in question.
A patch test, on the other hand, involves placing a patch containing the allergens on your arm or back so that the allergens can be absorbed by the skin. This process typically takes 72 hours to complete and will require a return visit to the allergist’s office.
Through a laboratory analysis of a small blood sample, the serum allergy test measures the amount of allergy-causing antibodies circulating in your bloodstream, which are called immunoglobulin E (IgE) antibodies. If the IgE antibodies of a specific allergen are detected, it may indicate an allergy to that substance.
Your doctor will use all the information available to them including results of testing (in combination with medical history) to help make the appropriate diagnosis. Because allergies can cause life-threatening reactions, it’s important that you work with your doctor to find the testing and treatment plan that works best for you.