 Body Surface Area
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Body Surface Area

In physiology and medicine, the body surface area (BSA) is the measured or calculated surface area 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, such as chemotherapy.

Typically there is a 4-10 fold variation in drug clearance between individuals due to differing the activity of drug elimination processes related to genetic and environmental factors. This can lead to significant overdosing and underdosing (and increased risk of disease 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.

## Uses

Examples of uses of the BSA:

There is some evidence that BSA values are less accurate at extremes of height and weight, where Body Mass Index may be a better estimate (for hemodynamic parameters).

## Calculation

Various calculations have been published to arrive at the BSA without direct measurement. In the following formulae, BSA is in m2, W is mass in kg, and H is height in cm.

The most widely used is the Du Bois, Du Bois formula, which has been shown to be equally as effective in estimating body fat in obese and non-obese patients, something the Body mass index fails to do.

${BSA}=0.007184\times W^{0.425}\times H^{0.725}$ A commonly used and simple one is the Mosteller formula:

${BSA}={\sqrt {\frac {W\times H}{3600}}}=0.016667\times W^{0.5}\times H^{0.5}$ or even simpler :${BSA}={\sqrt {W\times H}}/{60}$ or if Ht is height in m :${BSA}={\sqrt {W\times Ht}}/{6}$ Other formulas for BSA in m2 include:

 Haycock $0.024265\times W^{0.5378}\times H^{0.3964}$ Gehan and George $0.0235\times W^{0.51456}\times H^{0.42246}$ Boyd  $0.0003207\times \mathrm {weight} \mathrm {(g)} ^{(0.7285-0.0188\log _{10}{\mathrm {weight} \mathrm {(g)} })}\times H^{0.3}$ or equivalently $0.03330\times W^{(0.6157-0.0188\log _{10}{W})}\times H^{0.3}$ Fujimoto $0.008883\times W^{0.444}\times H^{0.663}$ Takahira $0.007241\times W^{0.425}\times H^{0.725}$ Shuter and Aslani $0.00949\times W^{0.441}\times H^{0.655}$ Schlich $0.000975482\times W^{0.46}\times H^{1.08}$ (women) $0.000579479\times W^{0.38}\times H^{1.24}$ (men)

A weight-based formula was proposed by Costeff and recently validated for the pediatric age group that does not include a square root, making it easier to use. It is [4W (kg) + 7]/[90 + W (kg)].

## Average values

Average BSA for children of various ages, for men, and for women, can be estimated using statistical survey data and a BSA formula:

Mean male BSA by age
Age or age group metric imperial
Neonate (newborn) 0.243 m2 2.612 ft2
2 years 0.563 m2 6.060 ft2
5 years 0.787 m2 8.471 ft2
10 years 1.236 m2 13.304 ft2
13 years 1.603 m2 17.255 ft2
18 years 1.980 m2 21.313 ft2
20-79 years 2.060 m2 22.173 ft2
80+ years 1.920 m2 20.667 ft2
Mean female BSA by age
Age or age group metric imperial
Neonate (newborn) 0.234 m2 2.519 ft2
2 years 0.540 m2 5.813 ft2
5 years 0.771 m2 8.299 ft2
10 years 1.245 m2 13.401 ft2
13 years 1.550 m2 16.684 ft2
18 years 1.726 m2 18.579 ft2
20-79 years 1.830 m2 19.697 ft2
80+ years 1.638 m2 17.631 ft2

The estimations in the above tables are based weight and height data from the U.S. NCHS National Health and Nutrition Examination Survey (2011-2014).

There was an average BSA of for 3,000 cancer patients from 1990 to 1998 in a European Organisation for Research and Treatment of Cancer (EORTC) database.

During 2005 there was an average BSA of for 3,613 adult cancer patients in the UK. Among them the average BSA for men was and for women was .