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-Malmö GFR equation for use with rescaled cystatin C (r-LMR) and validate it against measured GFR (mGFR) in the EKFC cystatin C cohort of children ( = 2,293) and adults ( = 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, P). Performance was compared with the EKFC-equation (EKFC), the CAPA cystatin C equation, the corresponding equations based on rescaled creatinine (r-LMR and EKFC) and the arithmetic mean of r-LMR and CAPA (r-LMR+CAPA), r-LMR and r-LMR (r-LMR), and EKFC and EKFC (EKFC). The overall P of r-LMR 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-LMR (P 87.4%, 95% CI 86.6%-88.1%). r-LMR and EKFC exhibited similar performance both overall and across subgroups of age, sex, GFR and BMI and in children. All three arithmetic mean equations had similar P-accuracy and generally performed better than the corresponding single-marker equations. Our results show that the Lund-Malmö 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.