Estimation of residual glomerular filtration rate in peritoneal dialysis patients using cystatin C: comparison with 51Cr-EDTA clearance

Background. Measuring glomerular filtration rate (GFR) is an important assessment in peritoneal dialysis patients. In clinical practice, it is commonly measured by calculating the mean of the urinary clearance of urea and creatinine (GFRUrCl) but this process is time consuming and unreliable. We wished to compare several estimates of GFR including residual GFR estimated from cystatin C (GFRCysC) using a published equation (Hoek), GFRUrCl and 51 Crethylenediaminetetraacetic acid (EDTA) clearance, in peritoneal dialysis patients. Methods. GFRCysC, GFRUrCl and 51 Cr-EDTA clearance were measured in 28 patients undergoing peritoneal dialysis in a single dialysis unit. Results. GFRCysC was related to GFRUrCl (Spearman’s rank correlation coefficient rs ¼ 0.44; P ¼ 0.0185) and to 51 Cr-EDTA clearance (rs ¼ 0.48; P ¼ 0.0099). GFRCysC values were significantly (P ¼ 0.0077) lower than 51 CrEDTA clearance results (mean bias � 19.7%). However, GFRCysC did not differ significantly (P > 0.05) from GFRUrCl. Conclusions. GFRCysC is related to GFRUrCl but has a significant negative bias against 51 Cr-EDTA. Given the known limitations of 51 Cr-EDTA in estimating GFR in renal failure, this study provides additional validation suggesting that cystatin C-estimated rGFR (GFRCysC) gives a reasonable estimation of GFR without the clinical problems associated with 24 h urine collections.