Body-surface area

In physiology and medicine, the body surface area (BSA) is the measured or calculated surface of a human body. For many clinical purposes BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass. Estimation of BSA is simpler than many measures of volume.

Uses

Examples of uses of the BSA:

• Renal function is usually fractioned over the BSA to gain an appreciation of the true required glomerular filtration rate (GFR);
• The Quetelet index uses a somewhat modified form of the BSA;
• The cardiac index is a measure of cardiac output divided by the BSA, giving a better approximation of the required cardiac output;
• Chemotherapy is often dosed according to the patient's BSA.
• Glucocorticoid dosing is also expressed in terms of BSA for calculating maintenance doses or to compare high dose use with maintenance requirement.

Calculation

Various calculations have been published to arrive at the BSA without direct measurement, starting in 1916. The most commonly used is the Mosteller formula, published in 1987:

Metric (weight in kg and height in cm):

${x}={\sqrt {\frac {{\mbox{weight}}\times {\mbox{height}}}{3600}}}$

Imperial (weight in pounds, height in inches):

${x}={\sqrt {\frac {{\mbox{weight}}\times {\mbox{height}}}{3131}}}$

Normal values

• 'Normal' BSA is generally taken to be 1.7 m².
• Average BSA for men: 1.9 m²
• Average BSA for women: 1.6 m²
• Average BSA for child (9 years): 1.07 m²
• Average BSA for child (10 years): 1.14 m²
• Average BSA for child (12-13 years): 1.33 m²