Supplementary Material for: Associations of Serum Uromodulin and Urinary Epidermal Growth Factor with Measured Glomerular Filtration Rate and Interstitial Fibrosis in Kidney Transplantation

Introduction: Noninvasive biomarkers that reflect tubular health and allow early recognition of accelerated graft fibrosis development are warranted. Serum uromodulin (sUmod) and urinary epidermal growth factor (uEGF) originate from kidney tubules and may reflect functional nephron mass. The aim of this study was to investigate the associations between sUmod and uEGF with measured glomerular filtration rate (mGFR) and kidney allograft interstitial fibrosis percentage (IF%) score. Methods: sUmod and uEGF measurements, mGFR by iohexol-clearance and kidney allograft biopsies were obtained from kidney transplant recipients (KTRs) included in the Omega-3 fatty acids in Renal Transplantation (ORENTRA) trial at 8 weeks (baseline) and at 1 year after transplantation (end of study). Associations were analyzed with univariable and multivariable linear regression. Results: Ninety patients at baseline and 48 patients at end of study had complete study variable assessments. uEGF normalized to urinary creatinine (uEGF/Cr) was associated with mGFR both at baseline (standardized β-coefficient [Std. β-coeff] = 0.457 [p = p = p = 0.002]). uEGF/Cr, sUmod, and mGFR were associated with graft IF% score both at baseline (Std. β-coeff = −0.349 [p = 0.001], −0.274 [p = 0.009] and −0.289 [p = 0.006], respectively) and at end of study (Std. β-coeff = −0.365 [p = 0.011], −0.347 [p = 0.016] and −0.405 [p = 0.004], respectively). The results remained largely unchanged in multivariable analysis. Conclusion: uEGF/Cr and sUmod were associated with mGFR and graft IF% score. Our results indicate a possible role of uEGF/Cr and sUmod in the follow-up of KTRs.