How do I calculate Body Surface Area (BSA)?

Body Surface Area (BSA) Calculation Methods

The Mosteller formula is recommended for calculating Body Surface Area (BSA) due to its simplicity and accuracy: BSA (m²) = √[(Height(cm) × Weight(kg))/3600] 1

Recommended BSA Formulas

The following formulas are validated for calculating BSA in clinical practice:

1. Mosteller Formula (Recommended for routine clinical use) 1, 2:

   • BSA (m²) = √[(Height(cm) × Weight(kg))/3600]
   • Advantages: Simple, easy to calculate, and accurate for most patients

2. Gehan and George Formula (Alternative, especially for pediatric patients) 1:

   • BSA (m²) = 0.0235 × (height [cm])^0.42246 × (weight [kg])^0.51456
   • Can also be expressed as: BSA (m²) = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425

3. Simple Weight-Based Formula for Children 3:

   • BSA (m²) = [4W(kg)+7]/[90+W(kg)]
   • Shows excellent correlation with the Mosteller formula (r²=0.991)

Clinical Applications of BSA

BSA calculations are critical in multiple clinical scenarios:

• Medication dosing: Particularly important for chemotherapeutic agents and medications with narrow therapeutic indices 1

• Renal function assessment: For calculating eGFR adjusted for body surface area, which is essential for drug dosing 4

  • The KDOQI Work Group recommends multiplying standardized eGFR by the patient's BSA/1.73 m² for pharmacologic dosing considerations

• Cardiac parameter indexing: Used by the European Heart Society for left ventricular size parameters and aortic measurements 1

Special Considerations

1. Consistency: When following patients over time, use the same formula consistently to avoid introducing artificial changes 1

2. Obese patients: Traditional formulas like DuBois may underestimate BSA by 3-5% in obese patients 2

3. Drug dosing: For medications with narrow therapeutic windows, BSA-adjusted calculations are particularly important 4

4. Height measurement: Actual height measurement should be obtained when possible, as estimations can introduce up to 7% variation 1

5. Renal function and drug dosing: For medications excreted by the kidneys, eGFR adjusted for an individual's BSA in mL/min (eGFRBSAadj) should generally be utilized 4

Practical Implementation

For most clinical scenarios, the Mosteller formula provides the best balance of accuracy and simplicity. It can be easily calculated using a standard calculator and has been validated across different populations 1, 2.

When height measurement is not available (particularly in pediatric settings), the weight-based formula can be used as an alternative for children 3.

For research purposes or when maximum precision is required, the Gehan and George formula may be considered due to its statistical robustness 1.

Remember that different BSA formulas can yield discrepancies of up to 0.5 m² for standard adult physique, with potentially significant clinical implications, especially for critical applications like chemotherapy dosing or renal function assessment 1.