Body fluid volume determination via body composition spectroscopy in health and disease

TLDR

Assessing extracellular, intracellular, and total body water is clinically important, and although bioimpedance spectroscopy offers usability advantages, systematic deviations in extreme body compositions highlight the need to validate BIS equations across diverse healthy and fluid‑imbalanced populations. This study introduces two BMI‑corrected Hanai‑theory equations for estimating extracellular and intracellular water, termed body composition spectroscopy (BCS). The equations were derived via cross‑validation on 152 subjects (120 healthy, 32 dialysis) from three centers and validated against bromide/deuterium dilution for ECW/TBW and total body potassium for ICW. BCS showed close agreement with reference methods (mean differences −0.4 L ECW, 0.2 L ICW, −0.2 L TBW) and improved standard error of estimate for ICW and TBW by 24–48 % compared to the standard Hanai approach, supporting its use across a wide range of body compositions.

Abstract

The assessment of extra-, intracellular and total body water (ECW, ICW, TBW) is important in many clinical situations. Bioimpedance spectroscopy (BIS) has advantages over dilution methods in terms of usability and reproducibility, but a careful analysis reveals systematic deviations in extremes of body composition and morbid states. Recent publications stress the need to set up and validate BIS equations in a wide variety of healthy subjects and patients with fluid imbalance. This paper presents two new equations for determination of ECW and ICW (referred to as body composition spectroscopy, BCS) based on Hanai mixture theory but corrected for body mass index (BMI). The equations were set up by means of cross validation using data of 152 subjects (120 healthy subjects, 32 dialysis patients) from three different centers. Validation was performed against bromide/deuterium dilution (NaBr, D2O) for ECW/TBW and total body potassium (TBK) for ICW. Agreement between BCS and the references (all subjects) was −0.4 ± 1.4 L (mean ± SD) for ECW, 0.2 ± 2.0 L for ICW and −0.2 ± 2.3 L for TBW. The ECW agreement between three independent reference methods (NaBr versus D2O−TBK) was −0.1 ± 1.8 L for 74 subjects from two centers. Comparing the new BCS equations with the standard Hanai approach revealed an improvement in SEE for ICW and TBW by 0.6 L (24%) for all subjects, and by 1.2 L (48%) for 24 subjects with extreme BMIs (<20 and >30). BCS may be an appropriate method for body fluid volume determination over a wide range of body compositions in different states of health and disease.