Reliability of Glomerular Filtration Rate Estimated by Creatinine-Based Formulas in Moderate to Severe Proteinuria

Background Creatinine-based Glomerular Filtration rate (GFR) formulas introduce a substantial bias in GFR estimations in patients with frank nephrotic syndrome. The bias and accuracy of creatinine-based GFR estimates (eGFR) in patients with non-nephrotic proteinuria need better characterization. Methods We utilized data from the Ramipril in non-diabetic renal failure (REIN 1) and REIN 2 trials involving non-diabetic chronic kidney disease (CKD) patients with proteinuria to compare eGFRs derived from the CKD Epidemiology Consortium (CKDEPI) formulas (with and without race), and the European Kidney Function Consortium (EKFC) equations with iohexol clearance (a gold-standard GFR measure, measured glomerular filtration rate [mGFR]). Bias was defined as the median difference between eGFR and mGFR, while accuracy was assessed using P30 and P15 metrics, which represent the percentage of eGFR values within ±30% and ±15% of mGFR, respectively.