Impact of obesity on the validity of body surface area (BSA) predicted by standard equations and measured by whole-body Magnetic Resonance Imaging

Background Until today, BSA is still based on formula calculation in clinical practice, because direct measurements remain laborious and time consuming. Different prediction equations are published with unclear validity in obese people. Measurement of BSA by whole body magnetic resonance imaging (MRI) may serve as a gold standard.

Methods The study population consisted of 70 subjects (35 women, 35 men, age 20–78 yrs, BMI 19.0-42.6 kg/m²). BSA was determined by analyzing circumference using the whole body transversal MRI images and the Java-based image analysis program ImageJ (NIH, ImageJ, 2017) was used. Circumferences of the images in cm were multiplied with the specific slice thickness. BSA results by MRI were compared to results from 8 existing BSA formulas. As a potential confounder of the bias, % fat mass was measured by air-displacement plethysmography.

Results Mean BSA measured by MRI was significantly higher in men compared with women (1.99 ±0.27 vs. 1.74 ±0.16 m², p < 0.001). In both sexes, BSA by MRI was lower than BSA predicted by different equations. In men, differences between BSA by MRI and different equations increased with increasing BMI and % fat mass whereas in women, with increasing BMI and % fat mass, these differences decreased. Age did not correlate with the bias of the prediction equations.

Conclusion Compared to BSA measured by MRI, BSA is overestimated by the different prediction equations in both sexes. This overestimation decreased with increasing overweight in men and increased with increasing overweight in women.

Publication History

Article published online:
16 June 2020