Accuracy of eight-polar bioelectrical impedance analysis for the assessment of total and appendicular body composition in peritoneal dialysis patients

Objective: To establish the accuracy of bioelectrical impedance analysis (BIA) for the assessment of total and appendicular body composition in peritoneal dialysis (PD) patients. Design: Cross-sectional study. Setting: University Nephrology Clinic. Subjects: In all, 20 PD patients and 77 healthy controls matched for gender, age and body mass index. Methods: Whole-body fat-free mass (FFM) and appendicular lean tissue mass (LTM) were measured by dual-energy X-ray absorptiometry. Resistance ( R) of arms, trunk and legs was measured by eight-polar BIA at frequencies of 5, 50, 250 and 500 kHz. Whole-body resistance was calculated as the sum of R of arms, trunk and legs. The resistance index ( RI) was calculated as the ratio between squared height and whole-body or segmental R. Results: RI at 500 kHz was the best predictor of FFM, LTMarm and LTMleg in both PD patients and controls. Equations developed on controls overestimated FFM and LTMarm and underestimated LTMleg when applied to PD patients. Specific equations were thus developed for PD patients. Using these equations, the percent root mean-squared errors of the estimate for PD patients vs controls were 5 vs 6% for FFM, 8 vs 8% for LTMarm and 7 vs 8% for LTMleg. Conclusion: Eight-polar BIA offers accurate estimates of total and appendicular body composition in PD patients, provided that population-specific equations are used.