Biomarkers of Renal Filtration: Evaluation and Transformation

Biomarkers of renal filtration sCr and CyC concentrations were analyzed using the Piccolo Xpress blood chemistry analyzer Comprehensive Metabolica Panel (Abaxis, Inc., Union City, CA, USA) and a commercial ELISA kit (R&D Systems, Minneapolis, MN, USA and Arbor Assays, Ann Arbor, MI, USA), respectively. The intra-assay precision for the ELISA kit was determined as 3.1% coefficient of variation (CV). eGFR (mL/min/1.73 m²) was determined using equations validated by the National Kidney Foundation [31 ]. uEGF concentrations were determined using a commercial ELISA kit (R&D Systems, Minneapolis, MN, USA) with an intra-assay precision of 2.5% CV. Urine creatinine (uCr) concentrations were determined by a colorimetric detection kit (Enzo Life Sciences Inc., Farmingdale, NY, USA). Each serum, plasma, and urine sample were allowed to thaw to room temperature prior to analysis, and all samples, controls, and standards were assayed in duplicate. The optical density of Elisa kit wells was determined using an ELx808 absorbance microplate reader set to 450 nm (Biotek, Winooski, VT, USA). uEGF ratio (uEGFR) was log₂ transformed to normalize the results [12 (link)]. Estimates of renal filtration were assessed using the Modification of Diet in Renal Disease (MDRD) and CKD-epidemiology equations using biomarkers SCr and CyC.