Screening for Food Allergies?
The recommendation: Don't perform screening panels for food allergies without previous consideration of medical history.
The rationale: Ordering broad screening panels for food allergens is not necessary and instead should be thoughtfully considered after eliciting a careful patient history. Sensitization is common, and only a minority of patients who test positive to an allergen are truly allergic and exhibit symptoms upon ingestion. When symptoms suggest a food allergy, tests should be selected based upon a careful medical history.
Medscape spoke with Scott H. Sicherer, MD, Professor of Pediatrics, Allergy, and Immunology at the Icahn School of Medicine at Mount Sinai in New York.
Medscape: The caveat to not order broad screening panels without consideration of medical history indicates that these broad panels are appropriate in some cases. After a careful history, are there children who still should be tested this broadly?
Dr. Sicherer: In most cases, a thorough medical history should lead to decisions to order specific individual tests, and only rarely "broad panels." Currently available serum tests measure immunoglobulin E (IgE) antibody specific to various foods. Having a positive test denotes "sensitization," an immune response. However, the "positive" test alone does not in itself diagnose an allergy. For example, roughly 8% of the population will register a positive IgE test to peanut, but the vast majority of these individuals are ingesting peanut without any illness. They have not been, nor will they ever be, allergic to peanut. It is also possible for a test to remain positive despite acquiring tolerance (resolution of an allergy). While a positive test does not intrinsically diagnose an allergy, the stronger the positive, the more likely there is a clinical allergy. In short, the test must be selected and interpreted in the context of a medical history.
Here is an example. Consider a child who ate a cookie containing egg, milk, wheat, and peanut ingredients and developed urticaria and vomiting in 10 minutes -- consistent with an allergic reaction. The child has only ingested peanut once before but had no complaints. He routinely tolerates wheat, milk, and egg. A "panel" test that includes common food allergens shows positives to milk, egg, and peanut with negatives to wheat and soy. This result could be concerning regarding allergy to egg and milk, but the history and tests more clearly suggest a peanut allergy because that food was rarely (once) ingested. The parents, however, become worried and also exclude milk and egg. The test therefore engendered unnecessary dietary exclusions leading to nutritional and social consequences. Rarely, exclusion of a tolerated food to which there is sensitization could also trigger a "new" allergy to the food. It would have been more appropriate to simply perform a test for peanut.
When might a "panel" test be appropriate? Consider the same child. The history additionally reveals the child tolerates beans (peanut is a bean) but has never ingested tree nuts. In fact, the bakery uses tree nuts, and there may have been tree nuts in the cookie. This may raise the question: Did peanut really cause the reaction, or was there a tree nut in the cookie? Because the child never ate nuts, a panel of tree nuts was obtained, and tests were extremely high to cashew and pistachio but undetectable to 7 other tree nuts. Now the question: Was a peanut allergy truly the culprit, or was a bit of cashew the trigger? Additional testing by an allergist revealed that indeed the child tolerates peanut. Had a thorough history and appropriate testing not been eventually undertaken, this child could have been at risk to be avoiding some foods unnecessarily while potentially not receiving the correct advice to avoid the true cause of his reaction.
Food allergy can be life-threatening and requires a careful diagnosis and proper education on avoidance and treatment of reactions. Diagnosis requires a detailed history and an understanding of the epidemiology of food allergy and test limitations. I recommend evaluation by a Board-certified allergist-immunologist to confirm and manage food allergy. There are several applicable clinical reports as well as a national guideline that are available to guide decisions about diagnostic evaluation and management.[6-8]