Relationship of serum cystatin C to peritoneal and renal clearance measures in peritoneal dialysis: A cross-sectional study

Background: Clinical management of peritoneal dialysis patients includes assessments of peritoneal and renal clearances of the low-molecular-weight endogenous solutes creatinine and urea. Cystatin C is a low-molecular-weight protein used as a glomerular filtration rate marker. We investigated whether serum cystatin C concentration is related to peritoneal and renal clearances of creatinine and urea. Study Design: Cross-sectional study. Setting & Participants: 119 patients undergoing peritoneal dialysis in a single dialysis unit. Predictor: Peritoneal, renal, and total clearance of urea as Kt/V-urea and creatinine as weekly creatinine clearance (C-Cr). Residual renal function (RRF) as the average of renal clearances of urea and creatinine. Outcomes & Measurements: Serum concentrations of cystatin C measured by using a particle-enhanced nephelometric immunoassay. Results: Serum cystatin C concentration was related inversely to RRF (Spearman rank correlation coefficient [r(s) = -0.65; P < 0.001), total weekly C-Cr (r(s) = -0.52; P < 0.001), and total Kt/V-urea (r(s) = -0.23; P = 0.01). In a multiple regression model, weight, normalized protein catabolic rate, and RRF had independent effects on serum cystatin C concentrations. Additional multiple regression models showed that only the renal components of Kt/V-urea and weekly CCr contributed to serum cystatin C concentrations. Limitations: Absence of reference GFR method. Conclusions: Serum cystatin C concentrations reflect predominantly renal, not peritoneal, clearance. Serum cystatin C measurement may be a simple and practical alternative to measurement of RRF Am J Kidney Dis 51:278-284. (c) 2008 by the National Kidney Foundation, Inc.