Gehan-George Formula – Body Surface Area Calculation
The Gehan-George formula calculates a person's body surface area using height and weight. It is widely used in medicine for accurate drug dosage calculations.
Things worth knowing about "Gehan-George Formula"
The Gehan-George formula calculates a person's body surface area using height and weight. It is widely used in medicine for accurate drug dosage calculations.
What is the Gehan-George Formula?
The Gehan-George formula is a mathematical equation used to estimate a person's body surface area (BSA). It was developed in 1970 by scientists E. A. Gehan and S. L. George and remains one of the most commonly used methods for BSA calculation in clinical medicine. Body surface area is expressed in square meters (m²).
The formula is:
BSA (m²) = 0.0235 × height (cm)^0.42246 × weight (kg)^0.51456
It is considered more accurate than the older and more widely known DuBois formula, as it was developed using a larger dataset and demonstrates greater precision across a wider range of body types.
Applications of the Gehan-George Formula
The primary application of the Gehan-George formula is in the calculation of drug dosages, particularly in oncology. Many chemotherapy agents are dosed not by body weight alone, but relative to body surface area, as this approach allows for more accurate and safer drug administration.
- Oncology: Calculation of chemotherapy doses (e.g., in mg/m²)
- Paediatrics: Precise dosing of medications in children and adolescents
- Nephrology: Estimation of glomerular filtration rate (GFR) to assess kidney function
- Cardiology: Normalisation of cardiac index and other haemodynamic parameters
- Intensive care: Calculation of fluid requirements and nutritional plans
Background and Development
The calculation of body surface area is based on the principle that human metabolism and the excretory capacity of certain organs -- such as the kidneys and liver -- correlate with body surface area. For many medications, especially those with a narrow therapeutic window (a small margin between effective and toxic doses), BSA-based dosing is therefore safer than weight-based dosing alone.
Gehan and George used data from 401 subjects to develop their formula and compared results with the reference measurements of the gold standard at the time. Compared to other formulas such as the DuBois formula (1916) or the Mosteller formula (1987), the Gehan-George formula shows higher precision particularly at extreme body measurements (very low or very high weight).
Calculation Example
For a person with a height of 170 cm and a weight of 70 kg, the Gehan-George formula yields a body surface area of approximately 1.83 m². This value is then multiplied by the desired dosage (e.g., 100 mg/m²) to determine the individually correct amount of medication.
Comparison with Other Formulas
Several formulas exist in clinical practice for calculating body surface area. The most common ones include:
- DuBois formula (1916): Historically significant, but developed on a small dataset; can be inaccurate at extreme body measurements.
- Mosteller formula (1987): Very easy to calculate (square root of [height × weight / 3600]); frequently used in practice due to its simplicity.
- Gehan-George formula (1970): Larger dataset, higher accuracy, especially for below-average or above-average body measurements.
- Haycock formula (1978): Considered particularly precise in the paediatric setting.
Relevance for Patients
For patients, the Gehan-George formula is primarily a tool applied in the background of medical treatment. In chemotherapy in particular, an accurate BSA-based dosage can make the difference between effective treatment and unnecessary side effects. Doses that are too high can cause serious adverse effects, while doses that are too low may reduce the effectiveness of the therapy.
Physicians and pharmacists apply the formula automatically during treatment planning; patients do not need to perform any calculations themselves.
References
- Gehan E.A., George S.L. (1970): Estimation of human body surface area from height and weight. Cancer Chemotherapy Reports, 54(4): 225-235.
- Mosteller R.D. (1987): Simplified calculation of body-surface area. New England Journal of Medicine, 317(17): 1098.
- Lam T.K., Leung D.T. (1988): More on simplified calculation of body-surface area. New England Journal of Medicine, 318(17): 1130.
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