Blood testing to determine a link between food and illness is increasingly common, but some tests are not considered diagnostic and can lead to confusion, according to a primer in CMAJ (Canadian Medical Association Journal).
Both traditional physicians and holistic medicine practitioners may offer blood testing to diagnose adverse reactions to food. A food allergy is a specific immunologic reaction to a food that can be reproduced with exposure to the food in question. An intolerance is an adverse reaction without an immunologic response, such as lactose intolerance. However, "food sensitivity" is a general term that may be used for any symptom or response that is thought to be food related.
The distinctions between all of the above may not be clear to patients and can be misunderstood. Moreover, unstandardized food sensitivity tests, which can cost hundreds of dollars, are widely available and can be purchased by patients from a variety of health care providers as well as some pharmacies. One common type of blood testing uses a measure of immunoglobulin G (IgG) antibody binding to specific foods. However, the presence of these antibodies may be part of the normal human response and indicate tolerance to these foods, rather than an adverse reaction.
"Physicians should caution patients about the controversy surrounding testing for food sensitivity," writes Dr. Elana Lavine, Humber River Regional Hospital, Toronto. "Recent position papers from European and American allergy and immunology societies have emphasized the limitations and potential misuse of IgG4 testing, indicating that these tests are not appropriate for making a diagnosis of food allergy."
Patients may visit their doctors for advice after their test results indicate a host of foods to avoid. It is important for physicians to explain that there is no proven role for IgG testing in diagnosing food allergies or guiding food elimination plans.