Clinical utility of serum specific IgE food testing in general practice: A tertiary care experience

Abstract

Serum Specific IgE (SSIgE) testing is the preferred method for diagnosis of food allergy by Primary Care Physicians(PCPs). However, the diagnostic value of such tests, without a valid history, is questionable due to high false positive results. We tested the hypothesis that greater than 50% of positive food allergens according to Serum Specific Immunoassays do not correlate with a definitive food allergy. We performed a medical record review on 336 patients previously diagnosed with “food allergies” based on positive SSIgE ordered by PCPs. We compared these SSIgE results with an assessment from our tertiary care center Allergy specialists which included detailed history, skin prick testing and home/in office oral challenges. The top 10 foods tested by PCPs were milk, peanut, wheat, shrimp, soybean, codfish, walnut, egg, sesame, and scallop. 167 (49.7%) subjects had positive skin testing to one or more foods. Only 41(12.20%) had positive oral food challenges. Average total serum IgE per patient was 581IU/ml (ref: 100-300IU/ml). SSIgE assay was obtained only on 71 subjects in 2008 compared to 240 in 2018. False positive rate in our study is >80 % compared to >50% in the previous studies.A high average total serum IgE level/ patient related to nonspecific IgE and cross-reactive but clinically irrelevant allergen SSIgE might be a reason for false-positive IgE values for the specific food allergen.A rising trend for indiscriminate ordering of SSIgE in the last 10 years has caused not only the over diagnosis of food allergy but also an unnecessary cost of evaluation.