Phillipov G, Seaborn C J, Phillips P J
Queen Elizabeth Hospital, Woodville, South Australia 5011.
Osteoporos Int. 2001;12(1):49-54. doi: 10.1007/s001980170157.
The reproducibility of bone mineral density (BMD) measurements by dual-energy X-ray absorptiometry (DXA), based on 12 successive monthly determinations, was assessed in a group of 24 subjects (23 postmenopausal women, 1 man) using six trained operators. The variability (S2A) was calculated from both duplicate operator measurements and the standard error of estimate from nonparametric regression of the individual subject series. Robust estimates of SA from the 90th percentile of the sampling distribution of variances were calculated for the spine (25 mg/cm2), femur neck (20 mg/cm2) and total femur (15.5 mg/cm2) using the bootstrap technique. The critical difference for a significant decrease (p = 0.05) at the spine, femoral neck and total femur was estimated at 57, 46 and 36 mg/cm2 respectively. Estimation of S2A allowed calculation of the probability that the true BMD, for an observed BMD near the osteoporosis diagnostic threshold (T-score < -2.5), is not misclassified. Analysis of covariance established a significant operator-subject interaction at all sites, but only the total femur was associated with a significant difference between operators. The percentage of body fat was a significant covariate for the spine and total femur regions. ANOVA showed that the greater proportion of variance was instrument-related. The limitations of DXA as an analytical method are discussed.
在一组24名受试者（23名绝经后女性，1名男性）中，由6名经过培训的操作人员，基于连续12个月的测定，评估了双能X线吸收法（DXA）测量骨矿物质密度（BMD）的可重复性。通过重复操作人员测量以及个体受试者系列非参数回归的估计标准误差来计算变异性（S2A）。使用自助法，从方差抽样分布的第90百分位数计算出脊柱（25mg/cm²）、股骨颈（20mg/cm²）和全股骨（15.5mg/cm²）的SA稳健估计值。脊柱、股骨颈和全股骨处显著降低（p = 0.05）的临界差异分别估计为57、46和36mg/cm²。S2A的估计允许计算在骨质疏松症诊断阈值附近（T值＜-2.5）观察到的BMD时，真实BMD未被错误分类的概率。协方差分析在所有部位均建立了显著的操作人员-受试者交互作用，但只有全股骨与操作人员之间存在显著差异相关。身体脂肪百分比是脊柱和全股骨区域的显著协变量。方差分析表明，较大比例的方差与仪器相关。讨论了DXA作为一种分析方法的局限性。
