Estimation of Glomerular Filtration Rate in Elderly Chronic Kidney Disease Patients: Comparison of Three Novel Sophisticated Equations and Simple Cystatin C Equation

Estimating glomerular filtration rate (GFR) in elderly patients is a problem, since they are poorly represented in studies developing GFR equations. Serum cystatin C is a better indicator of GFR than serum creatinine in elderly patients. Therefore the aim of our study was to compare frequently used serum cystatin C based GFR equations with a gold standard ((51)CrEDTA clearance) in elderly chronic kidney disease (CKD) patients. 106 adult Caucasian patients, older than 65years (58 women, 48 men; mean age 72.5years), were included. In each patient (51)CrEDTA clearance, serum creatinine (IDMS traceable method) and serum cystatin C (immunonephelometric method) were determined. GFR was estimated using the Simple cystatin C, CKD-EPI cystatin C, CKD-EPI creatinine-cystatin C and BIS2 equation. Mean serum creatinine of our patients was 141.4 +/- 41.5mol/L, mean serum cystatin C 1.79 +/- 0.6mg/L, mean (51)CrEDTA clearance was 52.2 +/- 15.9mL/min per 1.73m(2). Statistically significant correlations between (51)CrEDTA clearance and all formulas were found (P<0.0001). In the receiver operating characteristic (ROC) curve analysis (cut-off for GFR 45mL/min per 1.73m(2)) no significant differences in diagnostic accuracy between all the before mentioned equations were found. Bland-Altman analysis for the same cut-off showed that CKD-EPI creatinine-cystatin C and BIS2 equation underestimated and CKD-EPI cystatin C and Simple cystatin C equation overestimated measured GFR. All equations lacked precision. Analysis of ability to correctly predict patient's GFR below or above 45mL/min per 1.73m(2) showed similar ability for all equations (P=0.24-0.89). All equations are equally accurate for estimating GFR in elderly Caucasian CKD patients. For daily practice Simple cystatin C equation is most practical.