Increased ratio of peritoneal effusion-to-serum potassium concentration in a dog with gastric perforation

Objective: To describe the clinical and laboratory findings of a dog with gastric perforation, resulting in a markedly increased peritoneal effusion-to-serum potassium ratio. Case Summary: A 6-year-old mixed breed neutered male dog presented with a right femoral fracture after being hit by car. The fracture was repaired surgically. Four days postoperatively, the dog developed peritoneal effusion, confirmed with ultrasonography. Peritoneal effusion analysis and serum biochemistry, performed concurrently, showed blood-to-effusion glucose difference >1.1 mmol/L [>20 mg/dL], suggesting the effusion was septic. The effusion-to-serum creatinine ratio was mildly increased (1.36) and the effusion-to-serum potassium ratio was markedly increased (>2.67). Combined, these findings were suggestive of a septic uroabdomen. A positive contrast retrograde urethrocystography did not reveal urine leakage from the lower urinary tract. An exploratory laparotomy revealed a gastric perforation in the pyloric area and an intact urinary tract. New Information Provided: Gastric perforation should be considered a differential diagnosis in dogs with an increased peritoneal effusion to serum potassium ratio.