Extending the Lund-Malmö Creatinine-Based GFR Equation to Cystatin C - Validation Results from the European Kidney Function Consortium (EKFC) Cohort of Children and Adults

The aim of the present study was to extend the creatinine-based Lund-Malm & ouml; GFR equation for use with rescaled cystatin C (r-LMRCys) and validate it against measured GFR (mGFR) in the EKFC cystatin C cohort of children (n = 2,293) and adults (n = 7,727). Rescaling was obtained by dividing each biomarker by a Q-value, representing the population-specific median biomarker level among healthy individuals. Validation included median bias/precision/accuracy (percent estimates within +/- 30% of mGFR, P30). Performance was compared with the EKFC-equation (EKFCCys), the CAPA cystatin C equation, the corresponding equations based on rescaled creatinine (r-LMRCr and EKFCCr) and the arithmetic mean of r-LMRCr and CAPA (r-LMRCr+CAPA), r-LMRCr and r-LMRCys (r-LMRMean), and EKFCCr and EKFCCys (EKFCMean). The overall P30 of r-LMRCys in adults was 86.2% (95% CI 85.4%-86.9%), which was 6.6 percentage points (pp; 95% CI 5.8-7.4 pp) higher than for CAPA and similar to r-LMRCr (P30 87.4%, 95% CI 86.6%-88.1%). r-LMRCys and EKFCCys exhibited similar performance both overall and across subgroups of age, sex, GFR and BMI and in children. All three arithmetic mean equations had similar P30-accuracy and generally performed better than the corresponding single-marker equations. Our results show that the Lund-Malm & ouml; GFR equation can be adapted for use with rescaled cystatin C with performance that is similar to the best-performing equations based on rescaled creatinine. The generality of the applied biomarker rescaling principle implies that the future demand for population- and biomarker-specific GFR estimating equations can be expected to decrease substantially.