Uroabdomen in cats: creatinine and potassium in the effusion
3-year-old neutered male cat hit by a car 36 hours ago. It is depressed, with abdominal pain, and has not been seen urinating. The bladder is not palpable. FAST ultrasound shows free abdominal fluid.
| Parameter | Result | Reference |
|---|---|---|
| Serum creatinine | 4.2 mg/dL | 0.8–2.0 |
| Effusion creatinine | 14.8 mg/dL | — |
| Serum potassium | 6.0 mmol/L | 3.5–5.5 |
| Effusion potassium | 12.6 mmol/L | — |
What is the most likely diagnosis?
chevron_right Show answer and explanation
A. Traumatic haemoabdomen
It is common after road traffic trauma, but does not concentrate creatinine or potassium in the effusion. The effusion haematocrit would be similar to that of blood.
B. Uroabdomen due to urinary tract rupture
Correct. Effusion creatinine at least twice serum (here 3.5:1) and effusion potassium almost twice serum (2.1:1; in cats > 1.9:1) confirm urine. The azotaemia and hyperkalaemia result from peritoneal reabsorption.
C. Acute kidney injury from hypoperfusion, with secondary transudate
Acute kidney injury would explain the azotaemia, but in a transudate creatinine and potassium equilibrate with blood; they do not concentrate in the fluid.
D. Bile peritonitis from gallbladder rupture
It is diagnosed with effusion bilirubin higher than serum (often with bile crystals), not with creatinine and potassium.
lightbulb Key takeaway
A palpable bladder or urination do not rule out uroabdomen. Always compare effusion and blood: creatinine > 2:1 (dog and cat) and potassium > 1.4:1 in dogs or > 1.9:1 in cats. Stabilise the hyperkalaemia and drain the abdomen before surgery.
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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.