Body Water, Total

Used to assess hydration status, guide fluid management, and track body composition changes.
Indicated for dialysis patients to monitor volume overload and adjust dry weight (RCT data supporting improved BP, arterial stiffness, and reduced fluid overload 1 [Level I evidence]), for obesity/sarcopenia evaluation, and for oncology/nutrition monitoring where shifts in total body water reflect malnutrition or treatment response 2 [Level II evidence].

Varies with age, sex, and adiposity; higher in lean and younger individuals, lower in obesity or advanced age. Hydration status, recent diuretics, and acute illness skew estimates. Bioimpedance can be inaccurate in edema, ascites, or extremes of BMI. Equations assume normal body composition and may misestimate TBW in sarcopenia or pregnancy. Interpret values alongside clinical context rather than in isolation.