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 (GFR(UrCl)) but this process is time consuming and unreliable. We wished to compare several estimates of GFR including residual GFR estimated from cystatin C (GFR(CysC)) using a published equation (Hoek), GFR(UrCl) and (51)Cr-ethylenediaminetetraacetic acid (EDTA) clearance, in peritoneal dialysis patients. METHODS GFR(CysC), GFR(UrCl) and (51)Cr-EDTA clearance were measured in 28 patients undergoing peritoneal dialysis in a single dialysis unit. RESULTS GFR(CysC) was related to GFR(UrCl) (Spearman's rank correlation coefficient r(s) = 0.44; P = 0.0185) and to (51)Cr-EDTA clearance (r(s) = 0.48; P = 0.0099). GFR(CysC) values were significantly (P = 0.0077) lower than (51)Cr-EDTA clearance results (mean bias -19.7%). However, GFR(CysC) did not differ significantly (P > 0.05) from GFR(UrCl). CONCLUSIONS GFR(CysC) is related to GFR(UrCl) 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 (GFR(CysC)) gives a reasonable estimation of GFR without the clinical problems associated with 24 h urine collections.