Serum cystatin C for estimation of residual renal function in children on peritoneal dialysis

Residual renal function (RRF) is an important parameter in the management of patients on chronic dialysis. The aim of this cross-sectional study was to determine the efficacy of serum cystatin C (CysC) for RRF estimation in 20 children (16 boys, 4 girls; median age 13.4 years) undergoing peritoneal dialysis (PD). For studies of correlation with serum CysC, the average of creatinine clearance rate (C_cr) and urea clearance rate (C_urea), Kt/V_urea, and weekly C_cr were evaluated as parameters reflecting RRF. The serum CysC level was found to be negatively correlated with urine volume (r = −0.717, P < 0.001), average of C_cr and C_urea(r = −0.851, P < 0.001), total and renal weekly C_cr (r = −0.795, P < 0.001; r = −0.845, P < 0.001, respectively), and renal Kt/V_urea (r = −0.793, P < 0.001) and positively correlated with peritoneal weekly C_cr (r = 0.738, P < 0.001) and peritoneal Kt/V_urea (r = 0.785, P < 0.001). There was no significant association with total Kt/V_urea (r = −0.335, P = 0.148). In non-anuric group of patients, serum CysC had no link to peritoneal Kt/V_urea (r = 0.573, P = 0.066), but was negatively correlated with renal Kt/V_urea (r = −0.609, P = 0.047). In the multiple regression analysis, renal Kt/V_urea significantly contributed to log CysC concentration rather than peritoneal Kt/V_urea. The results of this study suggest that serum CysC could be an appropriate marker for RRF, independent of total and peritoneal Kt/V_urea.