Pierre M. Braillon MD, PhD, Presenter: Nothing to Disclose

Pascale Pracros-Deffrenne, Abstract Co-Author: Nothing to Disclose

In overweight and obese patients it is important to estimate the body weight for which the bearing skeleton would be well adapted. Dual energy X-ray absorptiometry (DXA) is a good technique to assess the bone compartment (bone mineral content, BMC, and density, BMD) as well as the lean tissue mass (LTM) and fat mass (FM). However, the measured values for these parameters are dependent from the DXA system used. The aim of this work was to define, in these situations of overweighting (OW), the best way to analyze whole-body DXA data in order to get relevant results in clinical practice, whatever the DXA system is.  

Five hundred and seventy five patients who did not suffer from any other pathology than OW were enrolled in this study (age range: 2.9 y. - 18.7 y; mean body mass index: 29.4±5.5 kg/m²). From them, 485 (294 females) were scanned on a pencil-beam DXA system (Norland XR36®) while the other 90 subjects (52 females) were scanned on a fan-beam DXA system (Hologic Discovery®). Equations of correlation previously established from data obtained in controls were used to calculate in these patients:  1) the mean weight (Wskel) for which their skeleton would be well proportionate according to their total BMC less their head BMC; 2) the mean body weight in agreement with the BMC values measured in their arms (Wa) and legs (Wl). Wskel, Wa and Wl were compared then to the weight Wo = BMC+LTM+FMo, BMC and LTM being the measured patient values, and FMo being the theoretical fat mass value that provided a physiological equilibrium with LTM.

The values for the ratios Wo/Wskel, Wo/Wa, and Wo/Wl calculated from the results obtained on both DXA systems were similar and close to one. In females: Wo/Wskel = 1.03±0.13 and 1.01±0.10; Wo/Wa = 1.14±0.16 and 1.02±0.11; Wo/Wl = 1.05±0.16 and 1.03±0.10 - in males: Wo/Wskel = 1.02±0.12 and 1.01±0.07; Wo/Wa = 1.10±0.16 and 1.03±0.09; Wo/Wl = 1.04±0.15 and 1.01±0.11 (XR36 and Discovery, respectively).           

From this study conducted among 575 overweight and obese youths measured on 2 different DXA systems it was shown that the bearing skeleton would be adapted to the body weight which corresponded to a good equilibrium between lean tissue mass and fat mass.

 In the follow-up of overweight and obese children and adolescents, clinicians can consider the equilibrium between lean tissue mass and fat mass to define a healthy body weight.

Braillon, P, Pracros-Deffrenne, P, Whole-Body Dual-Energy X-ray Absorptiometry in Overweight and Obese Youths: Most Relevant Results in Clinical Practice.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11003080.html