Table 2

Some size descriptors used for determining doses in obese patients

Body size descriptorFormulaComment
Body mass index (BMI), kg/m2Total body weight (TBW)/height (m)2Fails to distinguish between adipose tissue and lean muscle mass, or sexes
Body surface area (BSA), m2Haycock:Commonly used in oncology to determine doses of cytotoxics
0.024265×height (cm)0.3964×TBW (kg)0.5378
Boyd: 4.688×TBW(0.8168–0.0154×log TBW)Does not distinguish between sexes
Mostellar: ((TBW×height (cm))/3600)½
Ideal body weight (IBW), kgVarious methods41:Accounts for sex, but not body composition
Adjusted body weight (ABW), kgIBW+factor×(TBW−IBW)Attempts to adjust for body composition
Often used for calculating doses of aminoglycosides
Lean body weight (LBW), kg*James' equation42:
  • 1.10×TBW−0.0128×BMI×TBW (males)

  • 1.07×TBW−0.0148×BMI×TBW (females)

Closely related to lean (fat-free) mass and corresponds to extracellular fluid, muscle, bone, vital organs
Semi-mechanistic model43:
  • (9270×TBW)/(A+B×BMI),

  • where A and B are:

  • 6680 and 216, respectively (males),

  • 8780 and 244, respectively (females)

Predicted normal weight (PNW), kg*1.57×TBW−0.0183×BMI×TBW−10.5 (males)Predicts the normal weight of an obese individual. Accuracy may diminish at extremes of height and weight
1.75×TBW−0.0242×BMI×TBW−12.6 (females)
  • * These body size descriptors have been developed from adolescent and adult subjects and have not been formally validated for children.