Water and Small Solute Excretion in Continuous Peritoneal Dialysis Patients with Lean Body Mass Exceeding 90% of Body Weight as Estimated from Creatinine Kinetics

Abstract

Lean body mass computed from creatinine kinetics (LBM) is an index of somatic nutrition and correlates with other nutrition indices in CAPD. However, LBM exceeding 90% of body weight (LBM/W ≥ 0.9) may be an index of non-compliance, rather than nutrition. To test this hypothesis, we analyzed fluid and solute excretion in 40 CAPD patients with LBM/W ≥ 0.9 (group A). The comparison group (group B) consisted of 885 CAPD patients with LBM/W < 0.9. Group A was younger (38.3±14.8 vs 54.7±14.7 yr) and had a lower percent of women (23.5% vs 41.1%) and diabetic subjects (17.5% vs 42.6%) than group B (at P ≤ 0.019). Group A also had lower body mass index (22.7±2.7 vs 25.8±5.1 kg/m² P <0.001) and serum albumin (33.0±6.7 vs 35.2±5.5 g/L, P = 0.014). Despite similar prescribed daily fill volumes (group A 8.3±2.4, group B 8.5±2.2 L/24 h) and similar D/P urea and creatinine values, group A had higher daily drain volume (11.0±3.6 vs 9.6±2.1 L/24 h, P < 0.001). Renal clearances were similar, while peritoneal and total clearances were apparently higher in group A. Creatinine excretion was higher in group A (27.4±5.1 vs 13.6±4.1 mg/kg x 24 h, P < 0.001), with a large part of the excess creatinine excretion in group A being accounted for by peritoneal excretion. The combination of an apparently high daily ultrafiltration volume (2.7 L/24 h on the average), unrealistically high creatinine excretion rate, and relatively poor nutrition (low body mass index and serum albumin) in group A is consistent with non-compliance. We suggest that the finding of LBM/W ≥ 0.9 during a clearance study in CAPD should trigger an investigation for non-compliance.