Small solute clearances and nutrition indices in obese patients on continuous peritoneal dialysis

To investigate the relationship between obesity, small-solute clearances, and nutrition in continuous peritoneal dialysis (CPD), we compared clearances and nutrition indices between 270 obese and 502 normal-weight CPD patients. Degree of obesity was classified by the ratio of body weight (W) to desired weight (DW) at the first clearance study. The DWs were obtained from the tables of the Metropolitan Life Insurance Company, assuming a medium skeletal frame. The obese patients (group I) had W/DW > 1.2 (1.38 +/- 0.17), and the normal-weight patients (group II) had 0.9 < or = W/DW < or = 1.2 (1.05 +/- 0.08). Nutrition indices derived from urea nitrogen and creatinine excretion were normalized by both W and DW. The following variables differed between group I (first value) and group II: sex (women: 48.2% vs. 33.9%), W (87.6 +/- 14.4 kg vs. 68.2 +/- 8.7 kg), body surface area (1.95 +/- 0.22 m2 vs. 1.77 +/- 0.16 m2), body water by method of Watson (41.2 +/- 7.7 L vs. 36.3 +/- 5.5 L), body mass index (31.8 +/- 3.9 vs 24.3 +/- 2.0), protein nitrogen appearance (PNA: 62.9 +/- 17.6 kg in 24 h vs. 57.7 +/- 15.7 kg in 24 h), PNA normalized to DW (1.08 +/- 0.29 g/kg in 24 h vs. 0.96 +/- 0.26 g/kg in 24 h), creatinine excretion (CrEx: 1111 +/- 396 mg in 24 h vs. 991 +/- 348 mg in 24 h), CrEx/W (12.6 +/- 3.7 g/kg in 24 h vs. 15.4 +/- 4.5 g/kg in 24 h), CrEx/DW (17.3 +/- 5.3 g/kg in 24 h vs. 15.1 +/- 4.8 g/kg in 24 h), lean body mass (LBM: 49.3 +/- 13.8 kg vs. 43.6 +/- 11.9 kg), LBM/W (0.56 +/- 0.12 vs. 0.64 +/- 0.15), and LBM/DW (0.77 +/- 0.18 vs 0.67 +/- 0.16), all at p < or = 0.034. Marginal differences (0.10 > p > 0.05) were found in the diabetes prevalence (53.0% vs. 40.8%), height (165.9 +/- 11.7 cm vs. 167.4 +/- 9.8 cm), and serum albumin (3.64 +/- 0.55 g/dL vs. 3.53 +/- 0.62 g/dL). No differences were found in age, duration of CPD until the first clearance study, percent of subjects with anuria, Kt/V urea, creatinine clearance, blood urea nitrogen, serum creatinine, and PNA normalized to W. Obese CPD patients tend to have better nutrition indices than do normal-weight CPD patients with similar small-solute clearances. In obese subjects, normalization by W creates inappropriately low values for nutrition indices derived from urea nitrogen and creatinine excretion. Normalization of those indices by DW appears preferable.