Blood Tests – False Positive?

Freedom Allergy, Allergy Doctor, Atlanta, Georgia

False Positive Food Allergies

While many medical offices use blood tests to evaluate allergies, board certified allergists rely on skin prick testing, which offers a more appropriate reflection of true allergies. Blood tests frequently show “false positive” results, and provide evidence of an allergy that is not accurate. Many times, families come to our office with blood results from another doctor’s office showing a food allergy, when they have never actually had an allergic reaction to that food. If you have a question of blood results, it would be best to discuss the findings with an allergist, to make sure you move forward with the best plan for your allergies. After all, why eliminate a food from your diet, when you are not actually allergic to that food?

Read more, from the American College of Allergy, Asthma and Immunology

Q. My son recently had an allergic reaction to peanut butter, causing immediate wheezing and requiring a visit to our local ED, so his primary care physician ordered some allergy blood tests. The tests showed that my son is allergic to peanuts, but also to wheat and milk. I was told I need to remove peanut, milk and wheat from his diet. Currently he eats wheat and drinks milk every day without any trouble. Do I really need to take these foods out of his diet? Will I harm him if I don t?

A. Your son should definitely continue to strictly avoid all foods containing peanut and maintain two epinephrine auto-injectors at all times. The good news is that he does NOT have to remove milk or wheat from his diet if he is able to eat these foods without symptoms. While food allergy is becoming more common, so is the over-diagnosis of food allergy. Your doctor likely ordered a test looking for allergic antibodies, called IgE, to a panel of foods. Another test that can be done to aid in the diagnosis of food allergy is allergy skin prick testing. It is very important to know that patients can have a positive blood or skin test to a food, however, without having an allergy to that food (i.e. false positive). A diagnosis of food allergy is best made when someone has both a positive allergy test to a specific food and a history of reactions that suggests an allergy to the same food. The gold-standard or best test to diagnose food allergy is an oral food challenge performed by an allergist. Your son s positive blood test to peanut, paired with his recent reaction, confirms peanut allergy but positive blood tests alone do not indicate food allergy.Sometimes providers order another type of antibody test to foods, called IgG, to foods. This unproven test does not ever indicate allergy and can lead to inappropriate diagnosis and unnecessary food avoidance diets.If you think your child may have a food allergy or if you have limited your diet based upon possible food allergies, I suggest you consult with an allergist. Allergists are pediatricians or internal medicine doctors that have completed two to three additional years of specialty training on diagnosing and treating allergic conditions.

Reference: Does My Son Really Have to Avoid Milk and Wheat? American College of Allergy, Asthma and Immunology. 2015. http://acaai.org/resources/connect/ask-allergist/Food-Allergies#section-825.

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