Introduction: Dual energy X-ray absorptiometry (DEXA) has been the cornerstone in the diagnosis of osteoporosis. Quantitative ultrasound (QUS) of calcaneus is easy to perform and cheaper than DEXA but prior studies have shown a limited correlation and agreement between the two tests. The purpose of this study was to assess calcaneal ultrasound as a screening test for osteoporosis.
Material and methods: Two-hundred-ninety-seven 70-years-old Icelandic women underwent a DEXA measurement of lumbar spine, left hip and whole body as well as QUS of left calcaneus. We assessed the correlation and agreement between the two tests and searched for the optimal cut-off point in QUS for the diagnosis of osteoporosis from sensitivity and specificity calculations and ROC curves. We also examined correlation between DEXA or QUS and anthropometric or biochemical measurements of bone markers. Finally, we compared the women who had sustained a fracture to those who had not with regard to DEXA and QUS.
Results: The correlation between DEXA at different sites and QUS ranged form 0.40 to 0.57 (Spearman's correlation coefficient) with the best correlation for left hip DEXA. The best sensitivity/specificity relationship of QUS in diagnosis of osteoporosis (WHO criteria) at the hip, was found for QUS T-score of -2.5; sensitivity 91.7%, specificity 49.0%, positive predictive value 25.8% and negative predictive value of 96.8%. Kappa-statistic showed a marginal agreement between the two tests (k=0.25, p<0.01). The correlation was generally stronger between DEXA and serum biochemical markers of bone turnover or weight than between QUS and these parameters but was in the same direction. Mean hip bone density and QUS results were lower in the group of women with history of fractures than the others, 0.731+/-0.112 g/cm(2) vs. 0.779+/-0.130 g/cm(2) (T-score -1.18+/-1.18 vs. -1.61+/-1.20, p=0.001) and T-score -3.12+/-0.94 vs. -2.40+/-1.22 (p=0.0001) for QUS.
Conclusions: Even though QUS is not a good test for diagnosing osteoporosis as defined by WHO criteria, it is a reasonable screening test with good sensitivity and fair specificity when using T-score of -2.5 as the cut-off point.