Body-surface area: Difference between revisions

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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==
The '''body-surface area''' (BSA) — that is, more precisely, the surface area of a human body or, equivalently, the size of its skin —
Examples of uses of the BSA:
is a physiological measure used in medicine.
*[[Renal function]] is usually fractioned over the BSA to gain an appreciation of the true required [[glomerular filtration rate]] (GFR);
On the average, the body-surface area is 1.7 m<sup>2</sup> (1.9 m<sup>2</sup> for men and 1.6 m<sup>2</sup> for women).
*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==
A common estimate is given by the ''Mosteller formula'':
Various calculations have been published to arrive at the BSA without direct measurement, starting in 1916. The most commonly used is the Mosteller formula, published in 1987:
<!-- <ref name="pmid3657876">
{{cite journal| author=Mosteller RD| title=Simplified calculation of body-surface area. | journal=N Engl J Med | year= 1987 | volume= 317 | issue= 17 | pages= 1098 | pmid=3657876
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=3657876 }}
</ref> see Bibliography -->


Metric (weight in [[kilogram|kg]] and height in [[centimetre|cm]]):
: <math> \text{BSA} (\mathrm m^2 ) = \sqrt { \text{weight} (\mathrm{kg}) \times \text{height}(\mathrm{cm}) \over 3600 }
 
                                  = \sqrt { \text{weight} (\mathrm{lb}) \times \text{height}(\mathrm{in}) \over 3131 } </math>
:<math>{x}= \sqrt\frac{\mbox{weight} \times \mbox{height} }{3600}</math>
''Remark:''
 
Conversion of metric to English units or vice-versa shows that the two formulas are not equivalent.
Imperial (weight in [[pounds]], height in [[inch]]es):
However, the difference is far below the expected error of the estimate and is therefore negligible.
 
The numbers 3600 and 3131 have probably been chosen for mnemonic reasons.
:<math>{x}= \sqrt\frac{\mbox{weight} \times \mbox{height} }{3131}</math>
 
==Normal values==
*'Normal' BSA is generally taken to be 1.7 m<sup>2</sup>.
*Average BSA for men: 1.9 m<sup>2</sup>
*Average BSA for women: 1.6 m<sup>2</sup>
*Average BSA for child (9 years): 1.07 m<sup>2</sup>
*Average BSA for child (10 years): 1.14 m<sup>2</sup>
*Average BSA for child (12-13 years): 1.33 m<sup>2</sup>

Latest revision as of 20:01, 11 September 2011

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The body-surface area (BSA) — that is, more precisely, the surface area of a human body or, equivalently, the size of its skin — is a physiological measure used in medicine. On the average, the body-surface area is 1.7 m2 (1.9 m2 for men and 1.6 m2 for women).

A common estimate is given by the Mosteller formula:

Remark: Conversion of metric to English units or vice-versa shows that the two formulas are not equivalent. However, the difference is far below the expected error of the estimate and is therefore negligible. The numbers 3600 and 3131 have probably been chosen for mnemonic reasons.

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