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. Nevertheless, there have been several important critiques of the use of BSA in determining the dosage of medications with a narrow therapeutic index like many chemotherapy medications. Typically there is a 4-10 fold variation in cytotoxic drug clearance between individuals due to differing activity of drug elimination processes related to genetic and environmental factors. This can lead to significant overdosing and even more perniciously to underdosing (and increased risk of cancer recurrence). It is also thought to be a distorting factor in Phase I and II trials that may result in potentially helpful medications being prematurely rejected. The trend to personalized medicine is one approach to counter this weakness. Estimation of BSA is simpler than many measures of volume.

Uses

Examples of uses of the BSA:

• Renal clearance is usually divided by 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:

The Dubois & Dubois formula::

${BSA (m^2)}=0.007184 \times {weight \mbox{ (kg)}}^{0.425} \times {height \mbox{ (cm)}}^{0.725} =\frac{{weight \mbox{ (kg)}}^{0.425} \times {height \mbox{ (cm)}}^{0.725}}{139.2}$

One commonly used formula is the Mosteller formula, published in 1987 and adopted for use by the Pharmacy and Therapeutics Committee of the Cross Cancer Institute, Edmonton, Alberta, Canada:

${BSA (m^2)}= \sqrt\frac{weight \mbox{ (kg)} \times height \mbox{ (cm)} }{3600} = \frac {weight \mbox{ (kg)}^{0.5} \times height \mbox{ (cm)}^{0.5} } {60}$

Other formulas include the Haycock formula:

${BSA (m^2)}=0.024265 \times {weight \mbox{ (kg)}}^{0.5378} \times {height \mbox{ (cm)}}^{0.3964}$

the Gehan and George formula:

${BSA (m^2)} = 0.0235 \times weight \mbox{ (kg)}^{0.51456} \times height \mbox{ (cm)}^{0.42246}$

the Boyd formula:

${BSA (m^2)} = 0.0003207 \times weight \mbox{ (g)}^{(0.7285 - 0.0188 \log_{10}{weight \mathrm{ (g)}})} \times height \mbox{ (cm)}^{0.3}$

or which is almost the same

${BSA (m^2)} = 0.0332965 \times weight \mbox{ (kg)}^{(0.6157 - 0.0816474 \operatorname{ln}\; {weight \mathrm{ (kg)}})} \times height \mbox{ (cm)}^{0.3}$

the Fujimoto formula

${BSA (m^2)} = 0.008883 \times height \mbox{ (cm)}^{0.663} \times weight \mbox{ (kg)}^{0.444}$

the Takahira Formula

${BSA (m^2)} = 0.007241 \times height \mbox{ (cm)}^{0.725} \times weight \mbox{ (kg)}^{0.425}$

the Schlich formula

${BSA (m^2)} = \begin{cases} 0.000975482 \times weight \mbox{ (kg)}^{0.46} \times height \mbox{ (cm)}^{1.08} & \mathrm{for\; women} \\ 0.000579479 \times weight \mbox{ (kg)}^{0.38} \times height \mbox{ (cm)}^{1.24} & \mathrm{for\; men} \end{cases}$

Average values

Average BSA is generally taken to be 1.73 m² for an adult.

Average BSA values
Neonate (Newborn)	0.25	m²
Child 2 years	0.5	m²
Child 9 years	1.07	m²
Child 10 years	1.14	m²
Child 12-13 years	1.33	m²
For men	1.9	m²
For women	1.6	m²

External links

• Online BSA Calculator Calculate body surface area using any of five formulas.
• BC Cancer network BSA calculation guidelines.
• Online Body Surface Area Calculator (Dubois Formula)
• Online Body Surface Area Calculator (Mosteller Formula)
• Web CoolTool to Calculate BSA using any of the five formulae