Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA.
J Bone Miner Res. 2012 Jan;27(1):119-24. doi: 10.1002/jbmr.506.
Major alterations in body composition, such as with obesity and weight loss, have complex effects on the measurement of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA). The effects of altered body fat on quantitative computed tomography (QCT) measurements are unknown. We scanned a spine phantom by DXA and QCT before and after surrounding with sequential fat layers (up to 12 kg). In addition, we measured lumbar spine and proximal femur BMD by DXA and trabecular spine BMD by QCT in 13 adult volunteers before and after a simulated 7.5 kg increase in body fat. With the spine phantom, DXA BMD increased linearly with sequential fat layering at the normal (p < 0.01) and osteopenic (p < 0.01) levels, but QCT BMD did not change significantly. In humans, fat layering significantly reduced DXA spine BMD values (mean ± SD: -2.2 ± 3.7%, p = 0.05) and increased the variability of measurements. In contrast, fat layering increased QCT spine BMD in humans (mean ± SD: 1.5 ± 2.5%, p = 0.05). Fat layering did not change mean DXA BMD of the femoral neck or total hip in humans significantly, but measurements became less precise. Associations between baseline and fat-simulation scans were stronger for QCT of the spine (r(2)= 0.97) than for DXA of the spine (r(2)= 0.87), total hip (r(2) = 0.80), or femoral neck (r(2)= 0.75). Bland-Altman plots revealed that fat-associated errors were greater for DXA spine and hip BMD than for QCT trabecular spine BMD. Fat layering introduces error and decreases the reproducibility of DXA spine and hip BMD measurements in human volunteers. Although overlying fat also affects QCT BMD measurements, the error is smaller and more uniform than with DXA BMD. Caution must be used when interpreting BMD changes in humans whose body composition is changing.
身体成分的重大变化，如肥胖和减肥，对双能 X 射线吸收法（DXA）测量骨矿物质密度（BMD）有复杂的影响。脂肪变化对定量计算机断层扫描（QCT）测量的影响尚不清楚。我们在一个脊柱体模周围用连续的脂肪层（最多 12 公斤）进行 DXA 和 QCT 扫描之前和之后。此外，我们在 13 名成年志愿者的身体脂肪增加模拟 7.5 公斤前后，用 DXA 测量腰椎和股骨近端 BMD，用 QCT 测量脊柱小梁 BMD。在脊柱体模中，DXA BMD 在正常（p<0.01）和骨质疏松（p<0.01）水平上随脂肪层的顺序线性增加，但 QCT BMD 没有明显变化。在人体中，脂肪分层显著降低了 DXA 脊柱 BMD 值（平均值±标准差：-2.2±3.7%，p=0.05）并增加了测量的变异性。相比之下，脂肪分层增加了人体 QCT 脊柱 BMD（平均值±标准差：1.5±2.5%，p=0.05）。脂肪分层对人体股骨颈或总髋的 DXA 平均 BMD 没有显著影响，但测量变得不那么精确。与基线和脂肪模拟扫描之间的相关性更强 QCT 脊柱（r(2)=0.97）比 DXA 脊柱（r(2)=0.87），总髋（r(2)=0.80），或股骨颈（r(2)=0.75）。Bland-Altman 图显示，脂肪相关误差在 DXA 脊柱和髋部 BMD 比 QCT 脊柱小梁 BMD 更大。脂肪分层在人体志愿者中引入误差并降低了 DXA 脊柱和髋部 BMD 测量的可重复性。虽然上层脂肪也会影响 QCT BMD 测量，但误差较小且更均匀。在解释身体成分发生变化的人类的 BMD 变化时必须小心。
