Objectives: Body composition changes occur in peritoneal dialysis (PD) due to abnormalities in nutrition and hydration. We investigated abnormalities of nutrition and hydration in PD patients compared with healthy controls by measurement of total body potassium (TBK) and body water compartments.
Design: Cross-sectional comparison study.
Methods: We measured TBK--an indicator of body cell mass--by whole body counting, total body water (TBW) by deuterium oxide dilution, and extracellular water (ECW) by bromide dilution in 29 PD patients and 32 controls.
Results: The absolute mean value of TBK for PD patients was not significantly lower than in controls. The ratios of observed TBK to predicted TBK from prediction formulas were compared. Equations used were those of Boddy, Bruce, Burkinshaw, and Ellis and our own equation derived from a local control database (Leeds). Observed/predicted ratios of TBK were significantly less in PD than in control subjects for all equations. Water volumes did not differ between PD and control groups. Observed/predicted ratios for TBK in PD patients correlated with serum potassium (Boddy r = 0.355, p = 0.06; Bruce r = 0.411, p < 0.05; Burkinshaw r = 0.457, p < 0.01; Leeds r = 0.412, p < or = 0.05; Ellis r = 0.356, p = 0.06) and tended to correlate with serum albumin (Bruce r = 0.343, p = 0.07; Burkinshaw r = 0.421, p < 0.05; Leeds r = 0.357, p = 0.06; Ellis r = 0.310, p = NS). There was no relationship with serum potassium in controls. Serum albumin in PD correlated with TBK (r = 0.445, p < 0.02), TBK/height (r = 0.419, p < 0.05), TBK/weight (r = 0.554, p = 0.002), and TBK/TBW (r = 0.586, p = 0.0001). Extracellular water/intracellular water (ECW/ICW) was inversely related to TBK (r = -0.455, p < 0.02 in PD; r = -0.387, p < 0.05 in controls) and to TBK/height (r = -0.446, p < 0.02 in PD; r = -0.411, p = 0.02 in controls). TBK/weight reduced with age in PD (r = -0.445, p < 0.02), as did TBK/TBW in PD (r = -0.463, p < 0.02). ECW/ICW tended to increase with age in PD (r = 0.351, p = 0.06).
Conclusions: Observed/predicted ratio of TBK is reduced in PD patients relative to healthy controls, indicating reduced body cell mass. Serum albumin and potassium reflect TBK indices in PD. Body water volumes did not differ between PD and controls, implying no overall abnormality in hydration in the PD group. However, ECW is relatively increased compared to ICW with decreasing TBK indices, suggesting relative ECW expansion with reduction in body cell mass.