TBW is approximately 60% in men and 50% to 55% in women.
TBW is lower in obese (50%) and higher in lean individuals (70%).

FENa+ is used to differentiate between renal and prerenal Acute Renal Failure.
FENa+ > 1% (> 0.01 fraction) indicates renal causes.
FENa+ < 1% (< 0.01 fraction) indicates prerenal causes.