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What is Body Surface Area?
The measured surface area of the body is termed as the Body Surface area or BSA
in physiology and medicine. Its normal value is considered to be 1.7m². This
parameter shows the metabolic mass rather than the body weight for clinical
purposes. This is because the unusual body adipose mass doesn't affect it. There
are numerous judgments related to BSA's use in the determination of medicine
dosage with a narrow therapeutic index, like chemotherapy, pharmacotherapy, etc.
BSA determination is essential for the dosages of some drugs that
need to be administered to a patient. It is also used in some cases to determine
fluid requirements administered
intravenously. There were many formulas developed in the past years for
calculating the Body Surface Area. The Mosteller formula is considered to be the most common body
surface area equation today. The New England Journal of Medicine published it
in the year 1987.
Different genetic and environmental factors affect the drug elimination process
in various individuals. Further, there are 4-10 fold variations possible. This results
in notable overdosing or underdosing, which also significantly increases the
chances of recurrence of the disease.
It is considered to be a distorting factor in Phase I and II trials, resulting
in the premature rejection of many helpful medications. The efficient method of
dealing with this variability is paramount.
What are classifications of Body Surface Area?:
Height and weight are not the only determinants of BSA. Age and gender are the
other prime factors. Here are the classifications:
1. For adult men, the average BSA is 1.9 m².
2. It is 1.6 m² for adult women.
3. In the case of newborn kids, it is 0.25 m²; for those of 2 years age, it is
0.5 m²; 10-year old kids average 1.14 m², and for those of 12-13 years of age, it is 1.33
m².
What is the difference between Body Mass Index (BMI) and Body Surface
Area(BSA)?:
Both these parameters have frequent usage in the healthcare sector but
are often
confused. Each of them provides us different information. First, let us consider
Body Mass Index (BMI) which is beneficial in determining how overweight a person
is. This reliable parameter is used for easily correlating it with the body fat
mass percentage. BMI accurately estimates the total fat rather than body weight.
Thus it helps in assessing the risk factors such as heart disease, high blood
pressure, gallstones, respiratory issues, some kinds of cancer and type 2
diabetes.
The only drawback of BMI is that it overestimates the fat in the case of
athletes as well as those with a muscular build. Even in the case of elderly
people and those who have muscle atropy, it can underestimate body fat. In order
to calculate the BMI, we take the bodyweight of the person in kilograms and
divide it by height squared, as mentioned below:
BMI= Weight/ Height0.5
Depending on the cardiovascular risk, BMI is categorized for the different
races, such as African-American race, Caucasian and Hispanic. But if we consider
the case of Asians and South East Asians, the parameter underestimates the
obesity risk because of which a lower threshold has to be used in such cases.
According to the NIH, the waist measurement along with the BMI in obese
and overweight adults is needed for abdominal obesity assessment. For example,
when the waist circumference exceeds 40 inches in men and 35 inches in women,
the risk of cardiovascular and metabolic disorders increases.
Now let us consider the BSA. As opposed to the BMI, BSA measures the total body
surface area for drug doses estimation or medical assessments. Du Bois developed
the first formula in the year 1916 after which many formulas were developed to
measure it. Among all of them, the Mostella formula is the easiest one for
memorizing as well as calculating and is therefore used in clinical trials.
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