Food tests in dogs with itchy skin and food allergies

Abstract

BACKGROUND: Identification of offending foods in dogs with adverse food reactions is usually based on "deterioration" during open food challenges. OBJECTIVES: To examine the placebo effect during double-blinded, placebo-controlled food challenges using a predefined set of criteria for relapse. ANIMALS: Twelve dogs with atopic dermatitis and adverse food reactions. MATERIALS AND METHODS: Dogs were serially challenged with 40 g/day of eight food items (beef, chicken, codfish, corn flour, cow's milk, hen's egg, lamb, wheat), for 1 week, each mixed with their elimination diet and water. An additional two challenges were placebo (elimination diet mixed with water). Owners and investigators were blinded to the challenges and the order of the 10 challenges was randomised for each dog. Relapse was defined as moderate-to-severe owner global assessment of challenge deterioration and/or > 100% increase of Canine Atopic Dermatitis Extent and Severity Index, 4th iteration (CADESI-04) score (with the score at the end being > 9) and/or > 100% increase of pruritus using a Visual Analog Scale (with the score at the end being > 1.9/10). RESULTS: Most (91.7%) dogs were positive to one to six challenges with food items, yet half of them also were falsely positive in one placebo challenge. Two dogs had only one placebo challenge. The number of positive challenges to foods did not differ between dogs with positive and negative placebo challenges. CONCLUSIONS AND CLINICAL RELEVANCE: The placebo effect during double-blinded food challenges creates doubts about the accuracy of the results of challenges with food items in this and in previous studies where open food challenges were used.