Comparison of bone mineral density and quantitative ultrasound of the calcaneus: site-matched correlation and discrimination of axial BMD status

The performance of quantitative ultrasound (QUS) and dual energy X-ray abso rptiometry (DXA) bone densitometry of the calcaneus have been compared, bot h in terms of site-matched correlation and their discriminatory ability to identify osteoporotic and osteoporotic or osteopenic subjects. 91 female su bjects (aged 56.9+/-9.6 years, 31-84 years) who were routinely referred for axial BMD assessment of the lumbar spine and femoral neck by DXA (Lunar DP X-L), consented to have additional measurements of QUS (McCue CubaClinical Mk II) and DXA (Lunar PIXI) of their left calcaneus. The site-matched corre lation between calcaneal BMD with QUS parameters were: (a) broadband ultras ound attenuation (BUA) alone, adj-R-2=62.7%, p<0.0001; (b) velocity (VOS) a lone, adj-R-2=48.4%, p<0.0001; and (c) BUA and VOS combined, adj-R-2=65.2%, p<0.0001. The site-matched correlations are towards the higher end of data reported by other researchers, indicative of the exacting measurement prot ocol implemented here. 30 subjects were categorized as normal, 38 being ost eopenic and 23 being osteoporotic. Optimum accuracies and odds ratios were obtained using logistic regression. The differences in accuracy between cal caneal BMD and calcaneal QUS parameters were statistically insignificant, w ith zero included within the confidence intervals, for the identification o f both (a) osteoporotic and (b) osteoporotic or osteopenic subjects. The od ds ratios for the discrimination of subject status achieved with calcaneal BMD were higher, although statistically insignificant, than achieved with t he QUS parameters. Receiver operator characteristic (ROC) analysis for the identification of subjects into the categories (a) and (b) above was perfor med. Areas under the ROC curve (AUC) (95% confidence intervals) for the leg it of the probability that a subject would be osteoporotic were: 0.814 (0.7 00, 0.928) for calcaneal BMD; 0.791 (0.673, 0.909) for BUA; 0.717 (0.588, 0 .846) for VOS; and 0.793 (0.675, 0.911) for BUA and VOS combined. For the i dentification of osteoporotic or osteopenic subjects, the ROC areas were: 0 .851 (0.774, 0.928) for calcaneal BMD; 0.773 (0.678, 0.868) for BUA; 0.783 (0.690 0.877) for VOS; and 0.778 (0.685, 0.871) for BUG and VOS combined. A gain, calcaneal BMD provided a higher, yet statistically insignificant, AUC than any QUS parameter. In conclusion, for the identification of subjects defined by World Health Organization criteria for axial BMD, the performanc e of BMD and QUS calcaneal parameters were statistically comparable. The ch oice of peripheral bone densitometry modality should therefore be made upon factors external, to their discriminatory performance.