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 C(Cr) 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.

Serum Cystatin C Does Not Predict Mortality or Treatment Failure in Peritoneal Dialysis: A Prospective Study.

UNLABELLED: ♦ BACKGROUND: Small solute clearance, especially that derived from residual renal function (RRF), is an independent risk factor for death in peritoneal dialysis (PD) patients. Assessment of solute clearance is time-consuming and prone to multiple errors. Cystatin C is a small protein which has been used as a glomerular filtration rate (GFR) marker. We investigated whether serum cystatin C concentrations are related to mortality in patients receiving PD. ♦ METHODS: New and prevalent PD patients (n = 235) underwent assessment of Kt/Vurea, RRF, weekly creatinine clearance (CCr), normalized protein catabolic rate (nPCR) and a peritoneal equilibration test (PET) at intervals. Blood was collected simultaneously for cystatin C measurement. Patients were followed for a median of 1,429 days (range 12 to 2,964 days) until death or study closure. Cause of death was recorded where given. Cox regression was performed to determine whether cystatin C had prognostic value either independently or with adjustment for other factors (age, sex, dialysis modality, diabetic status, cardiovascular comorbidity, Kt/V, CCr, RRF, nPCR or 4 h dialysate to plasma creatinine ratio (4 h D/Pcr) during the PET). The primary outcomes were all-cause mortality and treatment failure. ♦ RESULTS: There were 93 deaths. Increasing age and 4 h D/Pcr ratio, decreased RRF and presence of diabetes were significantly [p < 0.05] negatively associated with survival and treatment failure. Serum cystatin C was not related to either outcome. ♦ CONCLUSIONS: Serum cystatin C concentration does not predict mortality or treatment failure in patients receiving PD.