Total body water in health and disease: A look at end-stage renal disease

Abstract

Methods for determining body composition have improved over the past 20 years, greatly increasing the accuracy and ease of making these measurements. Body composition measurements may be useful in the clinical management of patients suffering from several diseases such as obesity, diabetes, metabolic syndrome and renal failure. The measurement of body composition may include direct or indirect measurements of total body water (TBW), body fat mass (FM), fat-free body mass (FFM) and bone mass, and sometimes of the distribution of fat between the visceral or subcutaneous compartments. The choice of method depends on which of these compartments is of interest, whether the measurement is for clinical purposes or research, and the degree of precision that is required. For the purposes of anthropometric measurement, for estimating adiposity, fat distribution and body composition, together with densitometry, isotope dilution, impedance measurement and imaging techniques are now available. For practical reasons, the direct measurement of body composition is essentially limited to research centres. For general uses, indirect methods of predicting body composition, such as the development of regression equations or the bioelectrical impedance analysis (BIA), have been based on anthropometric variables or electrical measurements. In the case of end-stage renal disease, TBW assessment by means of BIA has three main targets: (a) assessment of the body dry-weight; (b) evaluation of the nutritional status (considering TBW together with FM, FFM and body cell mass); (c) calculation of the dialysis adequacy. Currently available guidelines have underlined the need for sensitive measures of both nutritional and hydration status to prevent malnutrition and oedema in kidney patients; BIA represents an attractive clinical tool to detect early changes in body composition in this clinical setting.