Food allergy: why the dietary challenge is needed
3-year-old Labrador with non-seasonal pruritus. After 8 weeks on a strict hydrolysed diet, pruritus has fallen from 8 to 2 on the owner's scale. The owner proposes keeping the dog on this diet for life.
What is the next step?
chevron_right Show answer and explanation
A. Consider food allergy confirmed and keep the diet
The improvement may be due to other coincident factors: change of season, treatment of infections or better flea control. Without a challenge, the diagnosis is not confirmed.
B. Reintroduce the previous diet: if pruritus recurs (usually within 1–14 days) and resolves again on the elimination diet, it is confirmed
Correct. The challenge is essential for diagnosis. Afterwards, ingredients can be introduced one at a time (sequential challenges) to identify those tolerated and broaden options.
C. Run a food IgE serology to confirm
Serological tests are not reliable enough to diagnose food allergy or to confirm the diet result.
D. Introduce a new ingredient every day to broaden the diet
Reactions can take up to two weeks to appear; changing daily makes it impossible to know which ingredient causes them.
lightbulb Key takeaway
If pruritus improves only partially on the diet, food allergy and atopy may coexist. The challenge tells you how much of the problem is food-related and avoids keeping an unnecessary diet for life.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.