BMI and body surface area
Body mass index and body surface area (Mosteller, Du Bois, Haycock).
When to use
- Classifying weight status, indexing haemodynamic and echocardiographic measurements, and dosing drugs (notably chemotherapy) by body surface area.
Formula
BMI = weight (kg) / height (m)². Mosteller BSA = √(height cm × weight kg / 3600). Du Bois BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425.
Pearls and pitfalls
- BMI does not distinguish fat from lean mass and may misclassify muscular individuals; Mosteller is the most widely used BSA formula because of its simplicity.
References
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
- Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916;17:863–71.
Body Mass Index (BMI) is a widely used measure of body fat based on height and weight. It is calculated by dividing body weight in kilograms by the square of height in meters. BMI is relevant for medical prognostication as it serves as a quick, low-cost, and reliable screening tool for body composition, risk of type 2 diabetes, metabolic syndrome and specific cancers.
BMI and cardiovascular outcomes
- High BMI is associated with several health conditions:
- Type 2 diabetes
- Hypertension
- Coronary artery disease
- Heart failure
- Dyslipidemia (including high LDL, total cholesterol and triglycerides)
- Atrial fibrillation
BMI categories
The World Health Organization defines BMI categories as follows:
Underweight: Less than 18.5
Normal weight: 18.5 to 24.9
Overweight: 25 to 29.9
Obese: 30 and above
Limitations of BMI
Despite its widespread use, BMI has several limitations:
- It does not distinguish between fat, muscle, and bone mass.
- It does not indicate the types or distribution of body fat.
- It may not be accurate for all populations, particularly at the extremes of height and weight.
- BMI is particularly poor a predictor in South Asians, who have substantially elevated risk of cardiovascular disease and diabetes at BMI levels of 23 kg/m2 or higher.
Body surface area (BSA)
Body Surface Area is the total surface area of the body. It is often used in clinical settings because it is considered a more accurate indicator of metabolic mass than body weight alone.
BSA is utilized in various medical applications:
- Calculation of drug dosages, particularly in chemotherapy
- Determination of fluid administration
- Assessment of various hemodynamic and echocardiographic parameters.