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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 with the Dubois & Dubois formula. A commonly used formula is the Mosteller formula, published in 1987:

Metric (area in square metres from weight in kilograms and height in centimetres): ${x}= \sqrt\frac{\mbox{weight} \times \mbox{height} }{3600}$

half-English units (area in square metres from weight in pounds, height in inches): ${x}= \sqrt\frac{\mbox{weight} \times \mbox{height} }{3131}$

Another is the Haycock formula (in children): ${x}=0.024265 \times {weight \mbox{ (kg)}}^{0.5378} \times {height \mbox{ (cm)}}^{0.3964}$,

Du Bois & Du Bois, Arch Intern Med 1916;17:863: ${x}=(71.84 \times {weight \mbox{ (kg)}}^{0.425} \times {height \mbox{ (cm)}}^{0.725})/10000$,

Gehan EA, George SL, Cancer Chemother Rep 1970;54:225-235: $\mathrm{S} = 0.0235 \times height \mbox{ (cm)}^{0.42246} \times weight \mbox{ (kg)}^{0.51456}$ ,

Boyd's Formula: $\mathrm{S} = 0.0003207 \times height \mbox{ (cm)}^{0.3} \times weight \mbox{ (g)}^{(0.7285 - 0.0188 \log_{10}{weight \mathrm{ (g)}})}$.

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
• Average BSA for neonate: 0.25 m2
• Average BSA for 2 year old child: 0.5 m2

References

• Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098. PMID 3657876.
• Haycock GB, Schwartz GJ, Wisotsky DH Geometric method for measuring body surface area: A height-weight formula validated in infants, children and adults J Pediatr 1978;93:62-66