Editing Body surface area

{{Short description|Drug calculating formula}}
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 [[Clinical trial#Phases|Phase I and II trials]] that may result in potentially helpful medications being prematurely rejected.<ref>{{cite journal |author=Gurney H |title=How to calculate the dose of chemotherapy |journal=Br. J. Cancer |volume=86 |issue=8 |pages=1297–302 |date=April 2002 |pmid=11953888 |pmc=2375356 |doi=10.1038/sj.bjc.6600139 }}</ref><ref>{{cite journal |vauthors=Gao B, Klumpen HJ, Gurney H |title=Dose calculation of anticancer drugs |journal=Expert Opin Drug Metab Toxicol |volume=4 |issue=10 |pages=1307–19 |date=October 2008 |pmid=18798700 |doi=10.1517/17425255.4.10.1307|s2cid=73327796 }}</ref> The trend to [[personalized medicine]] is one approach to counter this weakness.

==Uses==
Examples of uses of the BSA:
* [[Renal function|Renal clearance]] usually divided by the BSA i.e. per 1.73 m² to gain an appreciation of the true [[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 effective 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.

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).<ref>{{cite journal |year=2012 |last1=Adler |first1=AC |last2=Nathanson |first2=BH |last3=Raguhunathan |first3=K |last4=McGee |first4=WT |title=Misleading indexed hemodynamic parameters: the clinical importance of discordant BMI and BSA at extremes of weight |volume=16 |issue=6 |pages=471 |journal=Critical Care |doi=10.1186/cc11876 |pmid=23273020 |pmc=3672608 |doi-access=free }}</ref>

==Calculation==
Various calculations have been published to arrive at the BSA without direct measurement. In the following formulae, BSA is expressed in [[meter|m]]<sup>2</sup>, weight (or, more properly, mass) W in [[kilogram|kg]], and height H in [[centimeter|cm]].

The most widely used is the Du Bois formula,<ref name='Du Bois1916'>{{cite journal | title = A formula to estimate the approximate surface area if height and weight be known | journal = Archives of Internal Medicine | date = Jun 1916 |vauthors=Du Bois D, Du Bois EF | volume = 17 | issue = 6 | pages = 863–71 | doi=10.1001/archinte.1916.00080130010002| url = https://zenodo.org/record/1423319 }} Reprinted in {{PMID|2520314}}</ref><ref name='Verbraecken2006'>{{cite journal | title = Body surface area in normal-weight, overweight, and obese adults. A comparison study | journal = Metabolism: Clinical and Experimental | date = Apr 2006 | first = J | last = Verbraecken |author2=Van de Heyning P|author3=De Backer W|author4=Van Gaal L | volume = 55 | issue = 4 | pages = 515–24 | doi = 10.1016/j.metabol.2005.11.004 | url = http://www.metabolismjournal.com/article/S0026-0495(05)00437-3/abstract | access-date = 2012-09-07 | pmid=16546483| url-access = subscription }}</ref> 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.<ref>{{cite journal |pmid=17028412 |year=2006 |last1=Sardinha |first1=LB |last2=Silva |first2=AM |last3=Minderico |first3=CS |last4=Teixeira |first4=PJ |title=Effect of body surface area calculations on body fat estimates in non-obese and obese subjects. |volume=27 |issue=11 |pages=1197–209 |journal=Physiological Measurement |doi=10.1088/0967-3334/27/11/012|bibcode=2006PhyM...27.1197S |s2cid=12141324 }}</ref>

:<math>{BSA}=0.007184 \times W^{0.425} \times H^{0.725} </math>

The Mosteller formula is also commonly used, and is mathematically simpler:<ref>{{cite journal | last1 = Mosteller | first1 = RD | year = 1987 | title = Simplified calculation of body-surface area | journal = [[N Engl J Med]] | volume = 317 | issue = 17| page = 1098 | pmid = 3657876 | doi=10.1056/NEJM198710223171717}}</ref>

:<math>{BSA }= \frac{\sqrt{W \times H}}{60} 
=  0.016667 \times W^{0.5} \times H^{0.5} </math>

Other formulas for BSA in m<sup>2</sup> include:

:{|
| Haycock<ref>{{cite journal | last1 = Haycock | first1 = GB | last2 = Schwartz | first2 = GJ | last3 = Wisotsky | first3 = DH | year = 1978 | title = Geometric method for measuring body surface area: A height-weight formula validated in infants, children and adults | journal = J Pediatr | volume = 93| issue = 1 | pages = 62–66 | doi = 10.1016/s0022-3476(78)80601-5 | pmid = 650346 }}</ref> || <math> 0.024265 \times W^{0.5378} \times H^{0.3964}</math>
|-
|Gehan and George<ref>Gehan EA, George SL, ''Cancer Chemother Rep'' 1970, 54:225-235</ref> &nbsp; &nbsp; || <math> 0.0235 \times W^{0.51456} \times H^{0.42246} </math>
|-
|Boyd <ref name='Boyd1935'>Boyd, Edith (1935). ''The Growth of the Surface Area of the Human Body.'' University of Minnesota. The Institute of Child Welfare, Monograph Series, No. x. London: Oxford University Press.</ref> || <math> 0.03330
  \times W^{(0.6157 - 0.0188  \log_{10} {W})} \times H^{0.3} </math>
|-
| &nbsp; &nbsp; or alternatively &nbsp; &nbsp; || <math> 0.0003207
 \times \mathrm{weight} \mathrm{(g)}^{(0.7285 - 0.0188 \log_{10}{\mathrm{weight} \mathrm{ (g)}})}
 \times H^{0.3} </math>
|-
|Fujimoto<ref name='Fujimoto1968'>{{cite journal | last1 = Fujimoto | first1 = S | last2 = Watanabe | first2 = T | last3 = Sakamoto | first3 = A | last4 = Yukawa | first4 = K | last5 = Morimoto | first5 = K | year = 1968 | title = Studies on the physical surface area of Japanese. 18. Calculation formulae in three stages over all ages | journal = Nippon Eiseigaku Zasshi | volume = 23 | issue = 5| pages = 443–50 | doi = 10.1265/jjh.23.443 | pmid = 5752712 | doi-access = free }}</ref> || <math> 0.008883  \times W^{0.444} \times H^{0.663} </math>
|-
|Takahira<ref name='Fujimoto1968' /> || <math> 0.007241  \times W^{0.425} \times H^{0.725} </math>
|-
|Shuter and Aslani<ref>{{cite journal | last1 = Shuter | first1 = B | last2 = Aslani | first2 = A | year = 2000 | title = Body surface area: Du bois and Du bois revisited | journal = European Journal of Applied Physiology | volume = 82 | issue = 3| pages = 250–254 | doi=10.1007/s004210050679| pmid = 10929220 | s2cid = 25764872 }}</ref> || <math> 0.00949  \times W^{0.441} \times H^{0.655} </math>
|-
|Lipscombe <ref>Lipscombe, Trevor, ''Body Surface Area Formula by Use of Geometric Means'' [[Medicina Internacia Revuo]] 2020, 29 (114):11-18</ref> &nbsp; &nbsp; || <math> 0.00878108 \times W^{0.434972} \times H^{0.67844} </math>
|-
|rowspan=2 | Schlich<ref name=Schlich>{{cite journal | last1 = Schlich | first1 = E | last2 = Schumm | first2 = M | last3 = Schlich | first3 = M | year = 2010 | title = 3-D-Body-Scan als anthropometrisches Verfahren zur Bestimmung der spezifischen Körperoberfläche | journal = [[Ernährungs Umschau]] | volume = 57 | issue = 4 | pages = 178–183 | url = https://www.ernaehrungs-umschau.de/print-artikel/12-04-2010-the-3d-body-scan-as-an-anthropometric-analysis-to-measure-the-specific-body-surface/ }}</ref> || <math>0.000975482 \times W^{0.46} \times H^{1.08} </math> &nbsp; &nbsp; &nbsp; (women)
|-
|<math>0.000579479 \times W^{0.38} \times H^{1.24} </math> &nbsp; &nbsp; &nbsp; (men)
|}

For any formula, the units should match. Mosteller pointed out that his formula holds only if the density is treated as a constant for all humans. Lipscombe, following Mosteller's reasoning, observed that the formulas obtained by Fujimoto, Shuter and Aslani, Takahira, and Lipscombe are suggestive of <math> {8/900}  \times W^{4/9} \times H^{2/3} </math>, which is dimensionally correct for the case of constant density. It equals <math> (2^3/3^2)  \times (W^{2/3} H) ^ {2/3} /100 </math>.

A weight-based formula that does not include a square root (making it easier to use) was proposed by [[Hanan Costeff|Costeff]] and recently validated for the pediatric age group. It is [4W (kg) + 7]/[90 + W (kg)].<ref>Costeff H, "A simple empirical formula for calculating approximate surface area in children.," ''Arch Dis Child'', vol. 41, no. 220, pp. 681–683, Dec. 1966.</ref><ref name=Furqan>{{cite journal|last=Furqan|first=M|author2=Haque, A|title=Surface area in children: a simple formula.|journal=Indian Pediatrics|date=December 2009|volume=46|issue=12|pages=1085–7|pmid=19430073}}</ref>

==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:<ref>{{cite web|last1=Georgiev|first1=Georgi|title=Body Surface Area Calculator|url=https://www.gigacalculator.com/calculators/bsa-calculator.php|website=Gigacalculator.com|access-date=17 March 2018}}</ref>
{| class="wikitable"
|+Mean male BSA by age
!Age or age group
! colspan="2" |metric
! colspan="2" |imperial
|-
|Neonate (newborn)
|0.243
!m<sup>2</sup>
|2.612
!ft<sup>2</sup>
|-
|2 years
|0.563
!m<sup>2</sup>
|6.060
!ft<sup>2</sup>
|-
|5 years
|0.787
!m<sup>2</sup>
|8.471
!ft<sup>2</sup>
|-
|10 years
|1.236
!m<sup>2</sup>
|13.304
!ft<sup>2</sup>
|-
|13 years
|1.603
!m<sup>2</sup>
|17.255
!ft<sup>2</sup>
|-
|18 years
|1.980
!m<sup>2</sup>
|21.313
!ft<sup>2</sup>
|-
|20–79 years
|2.060
!m<sup>2</sup>
|22.173
!ft<sup>2</sup>
|-
|80+ years
|1.920
!m<sup>2</sup>
|20.667
!ft<sup>2</sup>
|}
{| class="wikitable"
|+Mean female BSA by age
!Age or age group
! colspan="2" |metric
! colspan="2" |imperial
|-
|Neonate (newborn)
|0.234
!m<sup>2</sup>
|2.519
!ft<sup>2</sup>
|-
|2 years
|0.540
!m<sup>2</sup>
|5.813
!ft<sup>2</sup>
|-
|5 years
|0.771
!m<sup>2</sup>
|8.299
!ft<sup>2</sup>
|-
|10 years
|1.245
!m<sup>2</sup>
|13.401
!ft<sup>2</sup>
|-
|13 years
|1.550
!m<sup>2</sup>
|16.684
!ft<sup>2</sup>
|-
|18 years
|1.726
!m<sup>2</sup>
|18.579
!ft<sup>2</sup>
|-
|20–79 years
|1.830
!m<sup>2</sup>
|19.697
!ft<sup>2</sup>
|-
|80+ years
|1.638
!m<sup>2</sup>
|17.631
!ft<sup>2</sup>
|}
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).<ref>{{Cite web|url=https://www.cdc.gov/nchs/nhanes/index.htm|title=National Health and Nutrition Examination Survey|website=Cdc.gov|access-date=2018-03-17}}</ref>

There was an average BSA of {{nowrap|1.73 m<sup>2</sup>}} for 3,000 cancer patients from 1990 to 1998 in a [[European Organisation for Research and Treatment of Cancer]] (EORTC) database.<ref name='Sparreboom2003'>{{cite journal | title = Paclitaxel Pharmacokinetics, Threshold Models, and Dosing Strategies | journal = Journal of Clinical Oncology | date = 15 Jul 2003 |vauthors=Sparreboom A, Verweij J | volume = 21 | issue = 14 | pages = 2803–4 | doi = 10.1200/JCO.2003.99.038 | pmid=12860961| doi-access = free }}</ref>

During 2005 there was an average BSA of  {{nowrap|1.79 m<sup>2</sup>}} for 3,613 adult cancer patients in the UK. Among them  the average BSA for men was {{nowrap|1.91 m<sup>2</sup>}} and for women was {{nowrap|1.71 m<sup>2</sup>}}.<ref name='Sacco2010'>{{cite journal | title = The Average Body Surface Area of Adult Cancer Patients in the UK: A Multicentre Retrospective Study | journal = [[PLoS One]] | date = 28 Jan 2010 |vauthors=Sacco JJ, Botten J, Macbeth F, Bagust A, Clark P | volume = 5 | issue = 1 | page = e8933 | doi = 10.1371/journal.pone.0008933 | url = http://ukpmc.ac.uk/articles/PMC2812484/reload=0;jsessionid=VMxGfFGKF2er3zi0XF6N.4 | access-date = 2012-09-09 | pmid=20126669 | pmc=2812484| bibcode = 2010PLoSO...5.8933S | doi-access = free }}</ref>

==References==
{{Reflist}}

[[Category:Human physiology]]
[[Category:Area]]