Use of bioelectrical impedance techniques for monitoring nutritional status in patients on maintenance dialysis

Malnutrition continues to be an important correlate of survival in dialysis patients. Nutritional surveillance at the clinical level requires use of simple, reasonably accurate, and easily accessible techniques for multicompartmental body composition analysis. Unfortunately, although gold standard methodologies (body density by underwater weight, total body water by isotope dilution, bone mineral content by neutron activation, total body potassium by (40)K whole body gamma counting) provide very precise assessments, they are not applicable to routine clinical practice. Because of its availability and simplicity, bioelectrical impedance (BEI) has significant potential as a complement to standard anthropometric techniques in the nutritional monitoring of patients with chronic renal failure. Consistency of technique and standardization of BEI equipment are essential for reproducibility of results. Several studies have validated the use of total body water by BEI as a surrogate for isotope dilution methods in dialysis patients, whereas others have established an excellent correlation with the volume of distribution of urea as measured by urea kinetic volume. Bioimpedance analysis for measurement of lean body mass has been extensively evaluated in stable healthy populations, with results similar to those obtained using hydrodensitometry and total body potassium. In dialysis patients, accuracy is contingent on a stable hydration status and/or appropriate correction for changes in extracellular volume status over time. Recent publication of bioimpedance norms for the hemodialysis population allows better comparisons with the national reference population studied as part of the National Health and Nutrition Examination Survey III (US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics, Hyattsville, MD). BEI methodology is a practical bedside tool for assessment of body composition that provides more consistent and reproducible results than standard anthropometry alone.