Measurement of residual renal function in patients treated with continuous ambulatory peritoneal dialysis

Renal function contributes markedly to the adequacy of continuous ambulatory peritoneal dialysis (CAPD), The best way to measure it in clinical practice has not been established. Ten stable CAPD patients with residual renal function were investigated to compare the GFR measured as inulin clearance (Cl-i) with the creatinine clearance (Cl-c), the urea clearance (Cl-u), and with 0.5 (Cl-c + Cl-u). Thereafter, an analysis of whether the administration of cimetidine could improve the accuracy of these clearances was performed. Two clearance periods (CP) of 24 h were investigated. During CP-2, patients received 400 mg cimetidine twice daily, for a total dose of 1200 mg. Two h before the urine and dialysate collection period, inulin was administered iv, Calculations were done for each CP for Cl-i, Cl-c, Cl-u, Cl-c-Cl-i, the Cl-c/Cl-i ratio, and the tubular secretion of creatinine (TSc). No differences between CP-1 and CP-2 were present for urinary excretion of volume and solutes, and clearance rates of inulin and urea. The median TSc decreased from 0.71 mu mol/min (range, -0.24 to 5.90) in CP-1 to 0.30 mu mol/min (range, -0.18 to 0.64) in CP-2 (P < 0.05), Therefore, the median ratio of Cl-c/Cl-i decreased from 1.23 (range, 0.87 to 2.20) in CP-1 to 1.11 (range, 0.95 to 1.51) in CP-2 (P < 0.05). The median overestimation of the Cl-i in CP-1 by the Cl-c was 0.90 mL/min (range, -0.28 to 3.80) and by the 0.5(Cl-c + Cl-u) was 0.30 (range, -0.67 to 1.52), The median overestimation of Cl-i during cimetidine treatment in CP-2 was 0.43 mL/min (range, -0.21 to 1.20). The range, in differences between Cl-i and Cl-c, in CP-2 was smaller than that between Cl-i and 0.5(Cl-c + Cl-u) in CP-1. The difference between the clearance rate of inulin and creatinine or the combined clearance rate magnitude of the average GFR, it can be concluded that the administration of cimetidine improved the accuracy of measuring the GFR with the Cl-c in CAPD patients.