DXA body composition corrective factors between Hologic Discovery models to conduct multicenter studies.

BACKGROUND: Dual X-ray absorptiometry body composition measurements are widely used for clinical and research settings. It is well known that measurements vary across instruments, needing caution for longitudinal monitoring or multicentric studies. This study was to quantify intra- and inter-center variability of bone mineral content, bone mineral density, fat and lean body composition measurements between Hologic Discovery models in order to calculate the corrective factors to be applied for multicenter research projects. MATERIALS AND METHODS: A whole body phantom composed of materials representing the thickness and percentage of bone, lean and fat mass in the human physiological range was analyzed ten times in three different centers using dual energy X-ray absorptiometry scanners (Two Hologic Discovery QDR A and one QDR W). In addition, we used a morphometric vertebral phantom to monitor stability and a three steps block phantom to check accuracy. RESULTS: We found a good long-term stability and accuracy for the three devices. Intra-center coefficients of variation were within the range of the manufacturer acceptable values (bone mineral density: 1.40%, bone mineral content: 1%, area: 1.50%, fat mass: 0.89%, lean mass: 0.76%, total mass: 0.12%). Whereas the inter-center coefficient of variation exceeded 8% (bone mineral density: 8.18%, bone mineral content: 3.03%, area: 8.63%: fat mass: 3,92%, lean mass: 7.89%, total mass: 2.85%). CONCLUSION: Our study showed that the discrepancies across centers remain a major concern, particularly with regard to body composition results. Our study highlight the need of cross calibration between densitometers and proposes corrective factors evaluated from a whole body phantom to lead multicentric studies adjustment.

Relationships between muscle mass, strength and regional bone mineral density in young men.

PURPOSE: Although the relationship between body composition and bone mineral density (BMD) is well established, the relative contribution of appendicular lean mass (ALM) and fat mass (FM) to BMD has been rarely evaluated in young men. METHODS: We assessed 100 young men (age: 24.4±2.8 years, BMI: 23.4±2.81 kg/m2). Appendicular lean mass index (ALM/H2) (ALMI), fat mass index (FM/ H2) (FMI), percentage of body fat, BMD at lumbar spine (LS), total hip (TH), femoral neck (FN) and whole body (WB) were measured using DXA. Muscle strength was evaluated by handgrip strength. Pearson's correlations and interactions between all variables were assessed using stepwise regression analyses. RESULTS: ALM index (ALMI) was positively correlated with BMD at all sites (r = 0.62 for WB p<0.05, r = 0.54 for FN p<0.05, r = 0.64 for TH p<0.05, r = 0.56 for LS p<0.05) whereas FMI was not correlated to BMD values. Stepwise regression analyses showed that ALMI produced a significant and positive influence on BMD (ß = 0.07 for WB p<0.001, ß = 0.04 for FN p<0.001, ß = 0.06 for TH p<0.001). Conversely, FMI was negatively associated with BMD at all sites (ß = -0.02 for WB p<0.001, ß = - 0.03 for FN p<0.001, ß = - 0.03 for TH p<0.001, ß = - 0.07 for LS p<0.001). Handgrip strength and BMDs were significantly and positively associated at all sites. CONCLUSIONS: Our data suggest that BMD was positively associated with ALMI while negatively with FMI. We confirm that ALMI is the strongest factor associated with BMD in a population of young men.