Not All Blood Tests are the Same

Blood testing for food sensitivity is different than blood testing for food allergies

(RxWiki News) Individuals should be weary about blood tests for food allergies. A new study highlights the possible confusion and ineffectiveness of relying on a blood test for food allergies or food sensitivity.

According to researchers, blood tests for food allergies are becoming increasingly common. Despite the growing popularity, patients need to be aware of what blood tests can detect and the difference between testing for a food allergy and food sensitivity.

"Ask your doctor about signs and symptoms of food allergy."

The study was led by Elana Levine, M.D., from the University of Toronto. Doctors are using blood tests to diagnose food sensitivity, which is any type of negative reaction to food. This can lead to confusion by patients who may not understand the differences between an allergy, intolerance or sensitivity. Physicians need to better educate patients about what blood tests can and cannot diagnose.

A food allergy is a specific negative reaction to a particular food protein. The body believes a type of food protein is actually an irritant and that causes the immune system to respond and produce immunoglobulin E (IgE) antibodies that react to the protein in question. Common food allergies include shellfish, peanuts and eggs.

Food intolerance is similar to a food allergy but without the immune system response. The body reacts negatively to the food protein but does not produce IgE. Lactose intolerance is a common type of food intolerance.

According to Dr. Levine, some physicians and holistic doctors use blood tests for food sensitivity, which is totally different than either food allergies or intolerance. Sensitivity could mean any type of negative effect that is believed to be related to food. This confusion could lead to misinformed patients and improper treatment.

Blood tests to diagnose food sensitivity measures immunoglobulin G (IgG) and not food-specific IgE. While IgG binds to specific food protein, IgG may be a normal part of the body's immune system reaction that indicates food tolerance and not intolerance.

To test for food allergies, doctors would take a blood sample but also check a patient's medical history, order a skin prick test and issue oral food challenges to specific foods.

Dr. Levine uses a hypothetical example of a young child with atopic dermatitis, a type of eczema, whose family is vegetarian. The child is taken to a holistic care provider who uses a blood test to determine a food allergy to eggs, which would eliminate the main source of protein for the child. This could be problematic, notes Dr. Levine, because only 35 percent of people with atopic dermatitis have an allergic reaction to specific food. Oral food challenges, such as eating a small amount of eggs, could properly determine an allergy.

Blood testing for food sensitivity should not be used to determine food allergy. Patients being tested for food sensitivity should be educated by their doctors about the limitations of the blood test.

No funding information was provided.

This study was published in the March edition of the Canadian Medical Association Journal.

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Review Date: 
March 14, 2012