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.
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 expressed in
m2, weight (or, more properly, mass) W in
kg, and height H 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]
The Mosteller formula is also commonly used, and is mathematically simpler:[7]
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 , which is dimensionally correct for the case of constant density. It equals .
A weight-based formula that does not include a square root (making it easier to use) was proposed by
Costeff and recently validated for the pediatric age group. It is [4W (kg) + 7]/[90 + W (kg)].[15][16]
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:[17]
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).[18]
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.[20]
^Haycock, GB; Schwartz, GJ; Wisotsky, DH (1978). "Geometric method for measuring body surface area: A height-weight formula validated in infants, children and adults". J Pediatr. 93 (1): 62–66.
doi:
10.1016/s0022-3476(78)80601-5.
PMID650346.
^Gehan EA, George SL, Cancer Chemother Rep 1970, 54:225-235
^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.
^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.
^Furqan, M; Haque, A (December 2009). "Surface area in children: a simple formula". Indian Pediatrics. 46 (12): 1085–7.
PMID19430073.