Urine Epidermal Growth Factor as a Potential Biomarker of Functional Kidney Mass for the Evaluation of Kidney Transplant Donors and Recipients

Background: Serum creatinine (SCr) and the estimated glomerular filtration rate (eGFR) are limited biomarkers of kidney function. A kidney donor “loses” approximately 50% of the kidney mass, still, post-procedure SCr and eGFR recover to a value ≥60-70% baseline. The study aimed to evaluate urine epidermal growth factor (uEGF) as a better biomarker of kidney mass. Methods: We recruited 32 donor/receptor pairs and obtained their pre-donation/pre-transplantation demographics, and kidney function tests. After the kidney donation/transplantation procedure, we collected blood and urine samples on days 2, 30, 90, and 180. The course of uEGF and eGFR were evaluated by linear mixed models and expressed as a percentage of the baseline kidney donor values. Results: Kidney donors had a median age of 38 years (IQR 32-54), and 24 (75%) were female. Kidney recipients' median age was 36 years (IQR 29-46), 18 (56%) were male, 18 (56%) had kidney failure from an unknown cause, and 8 (25%) from glomerular disease. 27 (84%) corresponded to a first transplant and 5 (16%) to a second transplant. The baseline eGFR in kidney donors decreased immediately post-donation and then stabilized at 60-64% of their baseline eGFR from day 30. Conversely, uEGF decreased post-donation and stabilized at 45-47% of their baseline uEGF (closer to the theoretically 50% decrease after donation) (Figure 1B). In kidney recipients, the eGFR increased to a peak of 66% of the baseline eGFR of their kidney donor and remained at 60-63% over follow-up. Interestingly, uEGF in the kidney recipient remained at 29-33% of the baseline level of the kidney donor. Urine EGF (but not eGFR) in the recipient correlated with the allograft volume estimated by CT scan. Conclusion: Urine EGF is a potential biomarker of functional kidney mass to be used for the evaluation of kidney donors and kidney recipients. uEGF levels are better approximate to the theoretical 50% “loss” of kidney mass that occurs after donation.