Sheffield Kidney Institute

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 ⁵¹Cr-ethylenediaminetetraacetic acid (EDTA) clearance, in peritoneal dialysis patients.

Methods. GFR_CysC, GFR_UrCl and ⁵¹Cr-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 ⁵¹Cr-EDTA clearance (r_s = 0.48; P = 0.0099). GFR_CysC values were significantly (P = 0.0077) lower than ⁵¹Cr-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 ⁵¹Cr-EDTA. Given the known limitations of ⁵¹Cr-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.