Protein catabolic rate in CAPD patients: comparison of different techniques

Protein intakes of patients on continuous ambulatory peritoneal dialysis (CAPD) are estimated by protein catabolic rate (PCR) or dietary protein intake assessments (DPI). In this study we compared two approaches suggested by Randerson et al. for calculating PCR. One method incorporates urea generation rate (UG) and estimated dialysate protein losses (PCR), while the other includes UG and measured dialysate protein losses (PCR). We feel that calculating PCR2 is more convenient in practice. We studied 95 patients on CAPD, 49 men and 46 women, with a mean age of 56.5 years (range 26.6-84.5 years) and lean body mass of 41 kg (range 19-71 kg). Mean +/- SEM of PCR1, PCR2, and DPI were: 0.89 +/- 0.02, 0.86 +/- 0.02, and 0.90 +/- 0.04 g/kg standard weight (std wt)/day, respectively. PCR1 and PCR2 were highly and significantly correlated (r = 0.94, p = 0.0001). The difference of PCR1-PCR2 is plotted against dialysate protein loss, which reveals that PCR2 often underestimates PCR1 if dialysate protein loss is > 10 g/day, but this difference is minimum (< 0.1 g/kg standard weight/day) when the dialysate protein loss is < 15 g/day. We conclude that PCR2 is an easy and effective method to monitor nutritional status in the majority of CAPD patients as very few will have dialysate protein losses > 15 g/day.