Body surface area (BSA) is an estimate of a person’s total surface area based on weight and height, used to determine medication dosage and assess kidney and heart health. BSA can provide a more accurate picture of fat deposits than BMI, but factors such as muscle mass and excess skin can affect results.
Body surface area (BSA) is an estimate of a person’s total surface area, based on a calculation involving weight and height. A simple calculation multiplies weight by height, divides by 3.131 if measurements are in pounds and inches, or 3.600 if measurements are in meters and kilograms, and then takes the square root of the remaining number. This formula is known as the Mosteller formula and is popular with doctors for its ease of use and accurate results.
Body surface area testing can provide useful information about fat deposits on a patient’s body and is sometimes compared to body mass index (BMI). Some people find that body surface area creates a more accurate picture, as people who are unusually heavy for their height will have a correspondingly high surface area, illustrating fat deposition on their frames. The calculation is only an estimate and it is important to consider factors such as a patient who exercises a lot and may be heavier due to good musculature, as muscle tissue is very heavy.
People use body surface area to determine the dosage of some types of medications. Drugs such as chemotherapy must be calculated very carefully to ensure the appropriate dosage for a patient. Intravenous fluids are also commonly dosed based on body surface area. Healthcare professionals who determine drug dosages regularly may carry a small calculator to make it easier to accurately calculate doses for their patients.
This calculation can also be used for other situations. Healthcare professionals interested in determining a patient’s renal clearance to assess kidney health can use body surface area to get a clear idea of how much the kidneys are filtering in a given period of time. It can also be used in calculating cardiac index, comparing cardiac output to a patient’s size. This should be within a stable range, demonstrating that a patient has a healthy heart. If it is unusually low, there may be a problem with the patient’s heart function.
Certain factors can change body surface area and cause a patient’s actual surface area to differ from the number determined by calculation. People who have lost a lot of weight quickly, for example, may have large folds of skin that increase their surface area but aren’t revealed in a simple formula involving their weight and height.
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