Grapes and raisins cause acute kidney injury in dogs through an unknown mechanism. Even small quantities can be fatal in susceptible animals, making prevention critical.
Grape toxicity causes acute kidney injury that is profoundly painful and distressing. Dogs developing anuric (no urine output) kidney failure experience uremia, fluid accumulation, and systemic collapse. The unpredictability of which dogs will be severely affected means that any grape or raisin ingestion deserves immediate veterinary attention. Waiting for symptoms before acting delays treatment to the point where irreversible kidney damage has already occurred.