Self-limited, sodium-dependent osmotic diuresis causes polyuria after living donor kidney transplantation.

BACKGROUND AND HYPOTHESIS: Polyuria, defined as urine output exceeding 3 l per day, is common following living donor kidney transplantation, yet its frequency and mechanisms are unclear. This study investigates the pathophysiology and potential recipient- or donor-specific factors influencing post-transplantation polyuria.

METHODS

We retrospectively evaluated 35 consecutive living donor kidney transplantations performed at the University Medical Center Marburg between 2018 and 2024. Clinical and laboratory characteristics of recipients and donors as well as the daily routine blood tests and 24-hour urine collections of the first 10 days post-transplantation were analyzed.

RESULTS

Polyuria occurred in 69.7% of recipients on the first day post-transplantation, independent of residual diuresis, ischemia time, or donor pre-transplantation urine volume. Urine output decreased to normal within 10 days, with no differences in serum creatinine or urinary kidney injury markers between polyuric and non-polyuric patients. Mechanistically, polyuria was driven by sodium-dependent osmotic diuresis, with sodium excretion being the sole decisive driver of early post-transplantation urine volume.

CONCLUSIONS

Polyuria after living donor kidney transplantation occurred in nearly 70% of cases without affecting short-term graft function and is explained by sodium-dependent osmotic diuresis. No donor- or recipient-specific predictors could be identified. Careful volume management is crucial in managing this condition.