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

Abstract

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.

Keywords: living donor kidney transplantation; osmotic diuresis; polyuria.

Graphical Abstract

Figure 1:

The 24-h urine volume, creatinine clearance, and volume balance in living donor kidney transplant recipients during the first 10 days following transplantation. (a) Urine volume in the first 10 days after living kidney transplant. N = 33, single values. The blue line indicates the threshold of 3000 ml per day. (b) 24-h urine volume in polyuric vs. non-polyuric patients in the first 10 days after living donor kidney transplant defined by urine output on day 1. N = 23 vs. 10, two-way ANOVA with Sidak's multiple comparison test. (c) Serum creatinine and (d) creatinine clearance in polyuric vs. non-polyuric patients in the first 10 days after LDKT defined by urine output on day 1. N = 23 vs. 10, two-way ANOVA with Sidak's multiple comparison test. (e) Intravenously administered fluid volume and (f) volume balance (IV volume per 24 h − urine output per 24 h) in polyuric vs. non-polyuric patients in the first 10 days after LDKT defined by urine output on day 1. N = 23 vs. 10, two-way ANOVA with Sidak's multiple comparison test.

Figure 2:

Urine osmolality, and renal overall osmolyte excretion and free water clearance following LDKT. (a) Urine osmolality, (b) urinary osmolyte excretion rate, and (c) free water clearance in polyuric vs. non-polyuric patients in the first 10 days after LDKT defined by urine output on day 1. N = 23 vs. 10, two-way ANOVA with Sidak's multiple comparison test. Simple linear regression between urine volume and urine osmolyte excretion (UV 2Na2KUreaGlucose) on day 1 (d) and 10 (e) in polyuric vs. non-polyuric patients after LDKT (N = 22 vs. 9).

Figure 3:

Urine osmolyte excretion and fractional sodium and urea excretion following LDKT. Simple linear regression between urine volume and urinary sodium (UV Na) (a) and urea excretion (UV Urea) (b) on day 1 after LDKT in polyuric vs. non-polyuric patients (N = 22 vs. 10). (c) Urine osmolyte composition in polyuric and non-polyuric patients on day 1 after LDKT, N = 22 vs. 10, Unpaired t-test. Simple linear regression between urine volume and urinary sodium (UV Na) (d) and urea excretion (UV Urea) (e) on day 10 after LDKT in polyuric vs. non-polyuric patients (N = 20 vs. 8). (f) Urine osmolyte composition in polyuric and non-polyuric patients on day 10 after LDKT, N = 20 vs. 8, Unpaired t-test. (g) Fractional sodium excretion (FENa) in percent and (H) fractional excretion of urea (FEUrea) in polyuric vs. non-polyuric patients in the first 10 days after LDKT defined by urine output on day 1. N = 22 vs. 10, two-way ANOVA with Sidak's multiple comparison test. (i) FeNa and FEUrea ration of polyuric/non-polyuric patients during the first 10 days after LDKT defined by urine output on day 1. N = 22 vs. 10, two-way ANOVA with Sidak's multiple comparison test.