Clinical scenario| CKD | Renal transplant | Polyuria
A 9-year-old boy with end-stage kidney disease secondary to posterior urethral valves undergoes a living-related renal transplant. The graft produces urine immediately after reperfusion. During the first 24 hours, he develops marked polyuria (10 mL/kg/hour). He is hemodynamically stable, serum creatinine falls progressively, serum sodium is 146 mmol/L, and urine specific gravity is 1.003.
What is the most likely cause of his polyuria?
A. Acute tubular necrosis of the graft
B. Calcineurin inhibitor toxicity
C. Delayed graft function
D. Post-transplant osmotic diuresis
E. Urinary leak from ureteric anastomosis
Correct answer & Explanation:
Correct Answer: D. Post-transplant osmotic diuresis
Explanation
Marked polyuria during the first 24–72 hours after a successful kidney transplant is usually physiological and results from osmotic diuresis. The newly functioning graft excretes accumulated urea, sodium, and retained extracellular fluid from the pre-transplant period. In addition, transient tubular dysfunction reduces concentrating ability, resulting in dilute urine.
Patients require careful replacement of urine losses with intravenous fluids while avoiding volume depletion, which can compromise graft perfusion.
- A. Acute tubular necrosis of the graft – Usually causes delayed recovery of renal function with persistently elevated creatinine rather than brisk urine output.
- B. Calcineurin inhibitor toxicity – Typically develops later and presents with rising creatinine and hypertension, not immediate postoperative polyuria.
- C. Delayed graft function – Characterized by poor urine output and the need for dialysis within the first week.
- E. Urinary leak from ureteric anastomosis – May cause decreased urine output, pain, fluid collection, or rising creatinine rather than physiological polyuria.
Key Learning Point
Early polyuria after a successful renal transplant usually reflects good graft function and post-transplant osmotic diuresis. The priority is meticulous fluid and electrolyte replacement to maintain optimal graft perfusion.
