# Body Surface Area Calculator

# BSA Calculator

This calculator measures the total surface area of the body to determine the dosage of drugs or the amount of fluids. This measurement is used for medicinal purposes only.

## FORMULAS

1) DuBois D, DuBois DF. A formula to estimate the approximate surface area if height and weight be known. Arch Int Med 1916;17:863-71.Equation: BSA (m2) = 0.007184 x Height(cm)0.725 x Weight(kg)0.425

2) Gehan EA, George SL. Estimation of human body surface area from height and weight. Cancer Chemother Rep 1970;54:225-35.

Equation: BSA (m2) = 0.0235 x Height(cm)0.42246 x Weight(kg)0.51456

3) 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;93:62-6.

Equation: BSA (m2) = 0.024265 x Height(cm)0.3964 x Weight(kg)0.5378

4) Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098.

Equation: BSA (m2) = SQR RT ( [Height(cm) x Weight(kg) ]/ 3600 )

### BACKGROUND

## 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.

Recommended references/reading:

www.kidney.org | https://www.epa.gov/ncea/efh/pdfs/efh-chapter06.pdfVerbraecken J, Van de Heyning P, De Backer W, Van Gaal L. Body surface area in normal-weight, overweight, and obese adults. A comparison study. Metabolism. 2006 Apr;55(4):515-24.

"Body surface area prediction with the commonly used DuBois formula underestimated BSA in obese patients by as much as 3% (male) to 5% (female)."

https://clincancerres.aacrjournals.org/cgi/content/full/10/24/8325?ck=nck

"The Du Bois formula was challenged in 1970 by Gehan and George who directly measured the skin surface area of 401 individuals. They found that the Du Bois formula over-estimated body surface area by 15% in ~15% of cases..."

https://www.ncbi.nlm.nih.gov/sites/entrez - See citation

"We recommend the Gehan-George equation, however, because it is based on direct measurements in over 400 subjects, including both children and adults. "