Used in clinical nutrition, sports medicine, and obesity management to distinguish between lean mass and fat mass.
In surgical or ICU settings, TBW helps optimize fluid management and monitor for conditions like third-spacing or fluid shifts due to sepsis or trauma.
Total Body Water (TBW) estimated in clinical practice:
These are rough estimates used in routine clinical settings:
Men:
TBW ≈ 60% of body weight
Women:
TBW ≈ 50–55% of body weight
Elderly or obese individuals:
Lower percentages are used (e.g., 45–50%)
Example:
A 70 kg male → TBW ≈ 0.6 × 70 = 42 liters
Knowing Total Body Water (TBW) helps guide fluid replacement therapy in dehydration by:
Dehydration involves a loss of body water. By knowing a person's TBW, clinicians can quantify how much water has been lost and how much is needed to restore balance.
Example Calculation:
A 70 kg man (TBW ≈ 60%) has about 42 L of TBW.
If he's estimated to be 5% dehydrated, then fluid deficit ≈ 5% of TBW:
→ 0.05 × 42 L = 2.1 L fluid deficit
TBW helps tailor fluid therapy based on:
Degree of dehydration (mild: 3–5%, moderate: 6–9%, severe: ≥10%)
Patient characteristics (age, weight, sex, comorbidities)
Fluid type (oral rehydration vs. IV crystalloids like normal saline or lactated Ringer's)
Replacing too little → persistent hypovolemia, organ hypoperfusion
Replacing too much → fluid overload, especially dangerous in heart or kidney disease
TBW estimates guide:
How much to replace in initial resuscitation (e.g., 1–2 L bolus in moderate-severe dehydration)
How much to give over maintenance and correction phases
When to slow or stop rehydration
A child with 10% dehydration and a weight of 20 kg:
Estimated TBW = 60% × 20 = 12 L
Deficit = 10% × 12 = 1.2 L → Replace this gradually over 24–48 hours, depending on the severity and setting.