Body composition analysis techniques in adult and pediatric patients: how reliable are they? How useful are they clinically?

Complex abnormalities of body composition occur in peritoneal dialysis (PD). These abnormalities reflect changes in hydration, nutrition, and body fat, and they are of major clinical significance. Clinical assessment of these body compartments is insensitive and inaccurate. Frequently, simultaneous changes of hydration, wasting, and body fat content can occur, confounding clinical assessment of each component. Body composition can be described by models of varying complexity that use one or more measurement techniques. "Gold standard" methods provide accurate and precise data, but are not practical for routine clinical use. Dual energy X-ray absorptiometry allows for measurement of regional as well as whole-body composition, which can provide further information of clinical relevance. Simpler techniques such as anthropometry and bioelectrical impedance analysis are suited to routine use in clinic or at the bedside, but may be less accurate. Body composition methodology sometimes makes assumptions regarding relationships between components, particularly in regard to hydration, which may be invalid in pathologic states. Uncritical application of these methods to the PD patient may result in erroneous interpretation of results. Understanding the foundations and limitations of body composition techniques allows for optimal application in clinical practice.