Comparison of QCT and DXA: Osteoporosis Detection Rates in Postmenopausal Women

Objective. To compare the osteoporosis detection rates in postmenopausal women when measuring bone mineral density (BMD) with quantitative computed tomography (QCT) in the spine versus dual X-ray absorptiometry (DXA) in the spine and hip and to investigate the reasons for the discrepancy between the two techniques. Methods. Spinal volumetric BMD was measured with QCT, and areal spinal and hip BMDs were measured with DXA in 140 postmenopausal women. We calculated the osteoporosis detection rate for the two methods. Lumbar CT images of patients who had a discrepancy between QCT and DXA findings were reviewed to evaluate vertebral fractures, spinal degeneration, and abdominal aortic calcification. Results. For the entire 140 patients, the detection rate was 17.1% for DXA and 46.4% for QCT, a significant difference (P < 0.01). Of the 41 patients with conflicting diagnoses, 7 whose diagnosis by QCT was osteoporosis had vertebral fractures even though their DXA findings did not indicate osteoporosis. Varying degrees of spinal degeneration were seen in all of the 41 patients. Conclusion. QCT may avoid the overestimation of BMD by DXA associated with spinal degeneration, abdominal aortic calcification, and other sclerotic lesions. It may be more sensitive than DXA for detecting osteoporosis in postmenopausal women.