Bone Mineral Density Assessment by DXA vs. QCT in Postmenopausal Females with Central Obesity

Objectives: Although Dual-energy X-ray Absorptiometry (DXA) is gold standard for osteoporosis diagnosis, several reports have shown discordant T-score values measured by Quantitative Computed Tomography (QCT) and DXA especially in obese subjects, but it is still not clear whether BMD measurement by two modalities is affected by overall obesity or central obesity in postmenopausal females. Therefore, the aims of this study were to compare BMD and T-scores by DXA and QCT and to evaluate whether these two osteoporosis assessment modalities yield different T-score values in postmenopausal females with obesity and central obesity.

Methods: This cross-sectional study enrolled 44 postmenopausal females, referred for osteoporosis screening. Anthropometric indices (BMI-body mass index, WC-waist circumference and ICOindex of central obesity) were measured and females underwent an assessment of bone mineral density by DXA and QCT.

Results: Lumbar Spine (LS) T-score values were observed to be significantly lower by DXA compared to qCT in females with BMI >25 kg/m2, (-1.9±1.5 vs. -2.3±1.2; p=0.039), in females with WC>88 cm(-1.9±1.5 vs. -2.4±1.2; p=0.008) and in females with ICO>0.5(-1.96±1.4 vs. -2.5±1.2; p=0.004). However, in normal-weight females and in those without central obesity, LS T-scores by DXA were not different than qCT. DXA at lumbar spine and proximal femur revealed osteoporosis in 47.7% and 11.4% respectively, while QCT detected osteoporosis in 61.4% of females (p<0.001). Measures of central obesity; ICO and WC were not associated with QCT bone mineral density (BMD) (r=0.14 and r=0.21, respectively), but were positively associated with both DXALS BMD (r=0.29 and r=0.31; p<0.05) and DXA proximal femur BMD (r=0.41 and r=0.44; p<0.01).

Conclusion: Our results suggest that obesity is associated with lower T-scores by DXA compared to QCT. Caution is needed when assessing osteoporosis status in obese postmenopausal females. However, further studies with larger sample size are needed to confirm the findings.