Body Surface Area

Body surface area is the surface of a human body that can be measured or calculated. In more literal terms, body surface area is the skin, which covers a human body. It is often difficult to measure one's surface area, thus body surface area is usually just an estimate based upon the height and weight of the person.

Body surface area is commonly used in medicine because it is an indicator of metabolic mass, as opposed to body weight, which can be skewed due to adipose tissue. Drug dosage and administration of IV medications is determined by body surface area. Some of the uses of body surface area include renal function, cardiac index, chemotherapy, and glucocorticoid dosing.

There are certain facts that may be correlated with body surface area. In mammals, body surface area may be correlated with basal metabolic rate, which is the rate at which energy is used by an organism when it is at complete rest. One's basal metabolic rate can be expressed as the calories that are used per square meter of body surface area per hour. Body surface area may also be correlated with blood volume in a warm-blooded animal. Aspects of the human body that are not correlated to body surface area are things such as glomerular filtration rate and liver function, both of which are related more to the internal working of each related organ.

Medically speaking, body surface area has been important in prescription drug dosing. An example of this is anticancer drug dosing; such dosing has been related [Page 274]to body surface area since the 1950s. Chemotherapy is a treatment that is offered and dosed using body surface area, rather than body weight, for two reasons. First, according to the National Cancer Foundation, body surface area has been shown to give a more accurate cross-species comparison of activity and toxicity for some drugs. Second, body surface area is more closely correlated to cardiac output. This is important because cardiac output determines how much blood flows to the liver and kidney, both of which influence how much drug is eliminated.

Body surface area is used as an indicator of metabolic mass instead of using body weight, which can be skewed due to adipose tissue.

If a drug dose is supposed to be related to body surface area, it is imperative that body surface area is carefully calculated. Although there are several formulas for calculating body surface area, one of the classic ways is the DuBois and DuBois formula, which was first developed in 1916. The formula is:

An average body surface area for a man is 1.9 square meters, and for a woman 1.6 square meters. An average 9-year-old child's body surface area is 1.07 square meters, while that for a 10-year-old child is 1.14 square meters.

Controversy has arisen in recent times because of the pharmacokinetics of drugs. Different individuals all have varying abilities to metabolize drugs. Therefore, even if drug doses vary with body surface area it is important to monitor the patient using other factors, such as glomerular filtration rate.

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