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Katie McCormack, MD: How is Food Allergy Evaluated?

This article is the second in a four-part food allergy series by allergist Katherine McCormack, MD. Click here for the first article.

If you or your child have had a concerning food reaction, I highly recommend speaking with an allergist. Allergists are trained to carefully record and evaluate a detailed personal medical history that includes the types of foods that have been ingested, frequency of food ingestion, reaction symptoms and timing, and other allergic conditions that you may have.

If allergy testing is recommended, a skin prick or scratch test is the most common initial examination to check for immediate allergic reactions to specific foods. In this test, your allergist will place a small drop of food extract into a very light scratch on your skin and monitor the area, typically for about 20 minutes. If a hive develops, you likely have an allergy to that particular food. If your skin does not react, it is unlikely that the food is a true allergen. 

In some instances, such as when the patient cannot stop taking their antihistamine medication or has severe skin eczema, a skin prick test may not be possible. In these cases, blood tests can assess the allergic antibodies.

False-positive results can occur with skin and blood testing, especially if there has not been a history of clinical reaction consistent with a food allergy. If the patient’s clinical history or testing is confusing, the allergist may perform an oral food challenge (OFC).

An OFC is a medical procedure in which pre-measured and incrementally larger doses of food are ingested in a stepwise fashion. An allergist and/or medical team trained in recognizing and treating anaphylaxis (a severe, potentially life-threatening allergic reaction) must oversee this challenge. You should never perform a food challenge at home due to the risk of a severe reaction.

About Katherine McCormack, MD

Allergy, Asthma & Immunology at Boulder Medical Center

Dr. Katie McCormack is an Allergy, Asthma, and Immunology Specialist at Boulder Medical Center. She treats infants, youth, and adults for everything from seasonal and food allergies to asthma and eczema. Dr. McCormack welcomes new patients for in-person and telehealth visits to her Louisville, Colo. clinic.

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