Definition of Body surface area

Body surface area: BSA. The total surface area of the human body. The body surface area is used in many measurements in medicine, including the calculation of drug dosages and the amount of fluids to be administered IV.

A number of different formulas have been developed over the years to calculate the body surface area and they give slightly different results. The most commonly used formula now is that of Mosteller, published in 1987 in The New England Journal of Medicine. According to Mosteller's "simplified calculation of body-surface area In metric terms" the body surface area = the square root of product of the weight in kg times the height in cm divided by 3600.

The "normal" body surface area is generally taken to be 1.7 m2 but, in actual fact, the body surface area depends on more than just height and weight. Other influential factors include the age and gender of the individual. For example:

  • Average body surface area for adult men: 1.9 m2
  • Average body surface area for adult women: 1.6 m2
  • Average body surface area for children (9 years): 1.07 m2
  • Average body surface area for children (10 years): 1.14 m2
  • Average body surface area for children (12-13 years): 1.33 m2

Body surface area is used for a determining other medical measures. As examples, renal function is measured by the glomerular filtration rate (GFR) which is calculated in regard to the body surface area. The cardiac index is a measure of cardiac output divided by the body surface area, giving a better approximation of the required cardiac output. Chemotherapy and pharmacotherapies are often dosed according to the patient's body surface area. Glucocorticoid dosing is also expressed in terms of body surface area for calculating maintenance doses or to compare high dose use with maintenance requirement.

Reference: Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098.

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