The Utility of Combined Urine Urea and Creatinine Clearance for Pretransplant Renal Function Assessment

BACKGROUND: Evaluation of donor renal function as glomerular filtration rate (GFR) is a crucial part of pretransplant workup. Most guidelines recommend measured GFR (mGFR) using exogenous markers with creatinine clearance (CrCl) as an alternative. However, exogenous markers are difficult to obtain and perform, and CrCl may overestimate GFR.

OBJECTIVE: We explore the use of CrCl and combined urea and creatinine clearance as an alternative for GFR assessment.

METHODS: A retrospective study involving 81 kidney donors from 2007 to 2020, with mGFR collected by chromium 51-labeled ethylenediaminetetraacetic acid (51Cr-EDTA) and CrCl and combined urea and creatinine clearance. We analyzed the performance of CrCl and combined urea and creatinine clearance against 51Cr-EDTA. Adequacy of urine volume was taken into consideration.

RESULTS: A total of 81 candidates with a mean age of 44.80 ± 10.77 years were enrolled. Mean mGFR from 51Cr-EDTA was 123.66 ± 26.91 mL/min/1.73 m2, and combined urea and creatinine clearance and CrCl were 122.13 ± 47.07 and 133.40 ± 36.32 mL/min/1.73 m2, respectively. CrCl overestimated 51Cr-EDTA. Though combined urea and creatinine clearance had minimal bias, it had a lower correlation coefficient (0.25 vs 0.43), lower precision (49.51 vs 38.10), and slightly lower accuracy within 30% of 51Cr-EDTA (74.07% vs 76.54%).

CONCLUSIONS: Combined urea and creatinine clearance did not improve the performance of CrCl. Nevertheless, it can potentially be used as first-line GFR assessment, followed by mGFR in selected donors, to ascertain threshold of safe kidney donation. A stringent urine collection method is essential to ensure accurate measurement.