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physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...
and
medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practice ...
, the body surface area (BSA) is the measured or calculated
surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ar ...
of a
human body The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a head ...
. 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 The therapeutic index (TI; also referred to as therapeutic ratio) is a quantitative measurement of the relative safety of a drug. It is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes ...
, such as
chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemother ...
. 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. The trend to
personalized medicine Personalized medicine, also referred to as precision medicine, is a medical model that separates people into different groups—with medical decisions, practices, interventions and/or products being tailored to the individual patient based on thei ...
is one approach to counter this weakness.


Uses

Examples of uses of the BSA: * Renal clearance usually divided by the BSA i.e. per 1.73 m² to gain an appreciation of the true
glomerular filtration rate Renal functions include maintaining an acid–base balance; regulating fluid balance; regulating sodium, potassium, and other electrolytes; clearing toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pr ...
(GFR); * The Quetelet index uses a somewhat modified form of the BSA; * The cardiac index is a measure of
cardiac output In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: t ...
divided by the BSA, giving a better approximation of the effective cardiac output; *
Chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemother ...
is often dosed according to the patient's BSA. *
Glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebr ...
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 Body mass index (BMI) is a value derived from the mass (weight) and height of a person. The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m2, resulting from mass in kilograms and hei ...
may be a better estimate (for hemodynamic parameters).


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, Reprinted in which has been shown to be equally as effective in estimating body fat in obese and non-obese patients, something the
Body mass index Body mass index (BMI) is a value derived from the mass (weight) and height of a person. The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m2, resulting from mass in kilograms and hei ...
fails to do. :=0.007184 \times W^ \times H^ The Mosteller formula is also commonly used, and is mathematically simpler: := \frac = 0.016667 \times W^ \times H^ Other formulas for BSA in m2 include: : 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 \times W^ \times H^ , which is dimensionally correct for the case of constant density. It equals (2^3/3^2) \times (W^ H) ^ /100 . 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 W (kg) + 7 0 + W (kg)


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: 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). There was an average BSA of for 3,000 cancer patients from 1990 to 1998 in a
European Organisation for Research and Treatment of Cancer The European Organisation for Research and Treatment of Cancer (EORTC) is a unique pan-European non-profit clinical cancer research organisation established in 1962 operating as an international association under Belgium law. It develops, conduc ...
(EORTC) database. During 2005 there was an average BSA of for 3,613 adult cancer patients in the UK. Among them the average BSA for men was and for women was .


References

{{Reflist Human physiology Area