Measurement of bone mass (BM), especially in the lumbar vertebrae, is very important for diagnosis of osteoporosis. In this study, we compared BM values measured by computed X-ray densitometry (CXD) with those by quantitative computed tomography (QCT), and discussed differences between the two methods.
The subjects were 90 women and 3 men, aged 42-86 years, who visited our outpatient department of osteoporosis. Metacarpal bone density (ΣGS/D) and metacarpal index (MCI) in the second metacarpal bone were measured by CXD. QCT was uesd for measurement of bone mineral density (BMD) in the lumbar trabecular bone, where pronounced osteoporotic changes occur early. The mineral values of L3 were expressed as mineral equivalent of CaCO³ in mg/ cm³, and≤75 mg/cm³ of L3 values were judged to be loss of lumbar BMD.
There were negative correlations between age and ΣGS/D, MCI or L3 value, and positive correlations were found between ΣGS/D or MCI and L3 value. Based on the above criterion of lumbar BMD loss, sensitivity and specificity of ΣGS/D for lumbar bone loss were examined. If ΣGS /D of 2.30 (T score -2.7) was used as the cut-off point, the sensitivity was 69.8% and the specificity was 75.0%, and if ΣGS/D of 2.37 (T score -2.3) and 2.40 (T score -2.1) were employed, the sensitivity was 79.1% and 79.1%, while the specificity was 64.5% and 62.5%, respectively. We concluded that BM values of cortical bone and trabecular bone decrease with age, and that sensitivity and specificity of GS/D for diagnosis of lumbar BMD loss are not very high.