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.^[1][2] The trend to personalized medicine is one approach to counter this weakness.

Uses

Examples of uses of the BSA:

• Renal clearance is 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).^[3]

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 formula,^[4][5] 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.^[6]

${BSA}=0.007184\times W^{0.425}\times H^{0.725}$

A commonly used and simple one is the Mosteller formula:^[7]

${BSA}={\sqrt {\frac {W\times H}{3600}}}=0.016667\times W^{0.5}\times H^{0.5}$ 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[8]	$0.024265\times W^{0.5378}\times H^{0.3964}$
Gehan and George[9]	$0.0235\times W^{0.51456}\times H^{0.42246}$
Boyd [10][11]	$0.0003207\times \mathrm {weight} \mathrm {(g)} ^{(0.7285-0.0188\log _{10}{\mathrm {weight} \mathrm {(g)} })}\times H^{0.3}$
or equivalently	$0.03330\times W^{(0.6157-0.0188\log _{10}{W})}\times H^{0.3}$
Fujimoto[12]	$0.008883\times W^{0.444}\times H^{0.663}$
Takahira[12]	$0.007241\times W^{0.425}\times H^{0.725}$
Shuter and Aslani[13]	${\displaystyle 0.00949\times W^{0.441}\times H^{0.655}}$
Schlich[14]	$0.000975482\times W^{0.46}\times H^{1.08}$       (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 [4Wkg+7]/[90+Wkg].^[15][16]

Average values

Average BSA for children of various ages, for men, and for women, are taken to be:

Neonate (newborn)			0.25	m²
Child of 2 years			0.5	m²
9 years			1.07	m²
10 years			1.14	m²
12–13 years			1.33	m²
Women			1.6	m²
Men			1.9	m²

There was an average BSA of 1.73 m² for 3,000 cancer patients from 1990 to 1998 in a European Organisation for Research and Treatment of Cancer (EORTC) database.^[17]

During 2005 there was an average BSA of 1.79 m² for 3,613 adult cancer patients in the UK. Among them the average BSA for men was 1.91 m² and for women was 1.71 m².^[18]

References

1. Gurney H (April 2002). "How to calculate the dose of chemotherapy". Br. J. Cancer. 86 (8): 1297–302. doi:10.1038/sj.bjc.6600139. PMC 2375356. PMID 11953888.
2. Gao B, Klumpen HJ, Gurney H (October 2008). "Dose calculation of anticancer drugs". Expert Opin Drug Metab Toxicol. 4 (10): 1307–19. doi:10.1517/17425255.4.10.1307. PMID 18798700.
3. Adler, AC; Nathanson, BH; Raguhunathan, K; McGee, WT (2012). "Misleading indexed hemodynamic parameters: the clinical importance of discordant BMI and BSA at extremes of weight". BioMed Central: Critical Care. 16 (6): 471. doi:10.1186/cc11876. PMC 3672608. PMID 23273020.
4. Du Bois D, Du Bois EF (Jun 1916). "A formula to estimate the approximate surface area if height and weight be known". Archives of Internal Medicine. 17 (6): 863–71. doi:10.1001/archinte.1916.00080130010002. Reprinted in PMID 2520314
5. Verbraecken, J; Van de Heyning P; De Backer W; Van Gaal L (Apr 2006). "Body surface area in normal-weight, overweight, and obese adults. A comparison study". Metabolism — Clinical and Experimental. 55 (4): 515–24. doi:10.1016/j.metabol.2005.11.004. PMID 16546483. Retrieved 2012-09-07.
6. Sardinha, LB; Silva, AM; Minderico, CS; Teixeira, PJ (2006). "Effect of body surface area calculations on body fat estimates in non-obese and obese subjects.". Physiological Measurement. 27 (11): 1197–209. doi:10.1088/0967-3334/27/11/012. PMID 17028412.
7. Mosteller, RD (1987). "Simplified calculation of body-surface area". N Engl J Med. 317 (17): 1098. doi:10.1056/NEJM198710223171717. PMID 3657876.
8. 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.
9. Gehan EA, George SL, Cancer Chemother Rep 1970, 54:225-235
10. Current, JD (1997). "A Linear Equation For Estimating The Body Surface Area In Infants And Children". The Internet Journal of Anesthesiology. 2 (2). doi:10.5580/1c6c. Retrieved 2016-03-16.
11. 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.
12. Fujimoto S, Watanabe T, Sakamoto A, Yukawa K, Morimoto K. Studies on the physical surface area of Japanese. 18. Calculation formulae in three stages over all ages. Nippon Eiseigaku Zasshi 1968;5:443–50.
13. Shuter, B; Aslani, A (2000). "Body surface area: Du bois and Du bois revisited". European Journal of Applied Physiology. 82 (3): 250–254. doi:10.1007/s004210050679.
14. Schlich, E; Schumm, M; Schlich, M (2010). "3-D-Body-Scan als anthropometrisches Verfahren zur Bestimmung der spezifischen Körperoberfläche". Ernährungs Umschau. 57: 178–183.
15. 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.
16. Furqan, M; Haque, A (December 2009). "Surface area in children: a simple formula.". Indian pediatrics. 46 (12): 1085–7. PMID 19430073.
17. Sparreboom A, Verweij J (15 Jul 2003). "Paclitaxel Pharmacokinetics, Threshold Models, and Dosing Strategies". Journal of Clinical Oncology. 21 (14): 2803–4. doi:10.1200/JCO.2003.99.038. PMID 12860961. Retrieved 2012-09-09.
18. Sacco JJ, Botten J, Macbeth F, Bagust A, Clark P (28 Jan 2010). "The Average Body Surface Area of Adult Cancer Patients in the UK: A Multicentre Retrospective Study". PLoS One. 5 (1): e8933. doi:10.1371/journal.pone.0008933. PMC 2812484. PMID 20126669. Retrieved 2012-09-09.