Body Water (Total Desired)
Info
Age Sex Factor Man Women Elderly Man Elderly Woman
Patient Weight
unit kg lb
Measured Na (mEq/L or mmol/L)
Normal Na (mEq/L or mmol/L)
R e s u l t s
Liters
? ? ?
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Info
Body Water (Total Desired)

Formula:

Body Water (Total desired) (TBW) in L= Measured serum [Na] × fraction of body weight × weight / Normal serum [Na]

  • Na conc in mEq/L or mmol/L
  • Weight in kg
  • Normal serum sodium remains constant - 140 mEq/L or mmol/L

The fraction of body weight is

  • Man = 0.6
  • Women = 0.5
  • Elderly Man = 0.5
  • Elderly Women = 0.45

Reference:

  1. Adrogué HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493-9.