The Authors Reply:

Abstract

We thank Drs Lindley and Lopot for their comments1.Lindley E. Lopot F. The use of bioimpedence to aid volume assessment in dialysis patients.Kidney Int. 2005; 87: 242Google Scholar and update on their current views of their previously described formula for normalizing the extracellular:total body water ratio.2.Lindley E. Devine Y. Hall L. et al.A ward-based procedure for assessment of fluid status in peritoneal dialysis patients using bioimpedance spectroscopy.Perit Dial Int. 2005; 25: S46-S48PubMed Google Scholar We wish to point out that our purpose for including this in our ‘mini-review’3.Davies S.J. Davenport A. The role of bioimpedance and biomarkers in helping to aid clinical decision-making of volume assessments in dialysis patients.Kidney Int. 2014; 86: 489-496Abstract Full Text Full Text PDF PubMed Scopus (213) Google Scholar was to give the reader an overview of the approaches taken to defining overhydration of dialysis patients in the scientific literature rather than assigning superiority to one or more of these approaches over another. There is a paucity of studies that make head-to-head comparisons of these different approaches, especially when linking them to either clinically important outcomes such as survival or determining their relative value in the management of surrogate endpoints such as left-ventricular hypertrophy. Even where these do exist there is no clear evidence of superiority. Recent examples include a direct comparison of multi- versus single-frequency bioelectrical impedance analysis (BIA) devices compared to the ‘gold’ standard isotope dilution techniques, which did not show a clear superiority of one over the other,4.Raimann J.G. Zhu F. Wang J. et al.Comparison of fluid volume estimates in chronic hemodialysis patients by bioimpedance, direct isotopic, and dilution methods.Kidney Int. 2014; 85: 898-908Abstract Full Text Full Text PDF PubMed Scopus (86) Google Scholar and other studies showing differences between patients from different ethnic groups and those with comorbidities including diabetes mellitus.5.Davenport A. Hussain Sayed R. Fan S. The effect of racial origin on total body water volume in peritoneal dialysis patients.Clin J Am Soc Nephrol. 2011; 6: 2492-2498Crossref PubMed Scopus (31) Google Scholar We completely agree that the formulas used to derive tissue hydration parameters on which any body composition model is based must be optimized for the specific device it was developed. However, there will always be a problem in using any formula that has been developed from population data—even assuming this was obtained from appropriate ethnically and comorbid matched subjects—to accurately describe the body composition of an individual. It follows that BIA devices must be used as an adjunct to clinical assessment of fluid status rather than as an independent and precise treatment target.