Serum cystatin C: a surrogate marker for the characteristics of peritoneal membrane in dialysis patients.

To evaluate whether cystatin C levels can be a surrogate marker of creatinine clearance and reflect the characteristics of peritoneal membrane in dialysis patients, we performed peritoneal equilibration tests (PET) in 18 anuric adult chronic peritoneal dialysis (PD) patients with a mean age of 39.7 +/- 20 years. All the samples were analyzed for urea, creatinine, and cystatin C. Peritoneal transport, mass transfer, and peritoneal clearance of cystatin C were calculated. Correlation and regression analysis was done using cystatin C as a dependent variable and age, sex, height, weight, body surface area, and creatinine as independent variables. Cystatin C demonstrated a significant time dependent increase of dialysate concentration and decline in the serum concentrations during PET, and a strong correlation between serum creatinine and serum cystatin C concentrations(r: 0.62, p= 0.008). The trans-peritoneal clearance (mL/min/1.73 m 2 ) of cystatin C was related to its serum concentration and was similar to creatinine in its pattern but of smaller magnitude. Peritoneal mass transfer (mg/4 hr per 1.73 m 2 ) for cystatin C serum creatinine was 1.68 +/- 0.67 and 73.3 +/- 29.8, respectively. The dialysis/plasma D/P cystatin C concentration was > or = 0.1 at 4 hrs of PET denoted high peritoneal transport, while the values of < 0.1 denoted low transport type. We conclude that cystatin C follows the same pattern of peritoneal exchange as creatinine but the magnitude of transfer is many folds lower than creatinine. At present clinical utility of cystatin C in the evaluation of solute clearance is probably limited due to the minute amounts transferred across the membrane and the high renal clearance in the presence of residual renal function.