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 even more perniciously to 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. Estimation of BSA is simpler than many measures of volume.
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].
Average BSA for children of various ages, for men, and for women, are taken to be:
Child of 2 years
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. 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. However, 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. 
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