Opportunistic Screening for Osteoporosis Using Abdominal Computed Tomography Scans Obtained for Other Indications

Background: Osteoporosis is a prevalent but underdiagnosed condition. Objective: To evaluate computed tomography (CT)-derived bone mineral density (BMD) assessment compared with dual-energy x-ray absorptiometry (DXA) measures for identifying osteoporosis by using CT scans performed for other clinical indications. Design: Cross-sectional study. Setting: Single academic health center. Patients: 1867 adults undergoing CT and DXA (n = 2067 pairs) within a 6-month period over 10 years. Measurements: CT-attenuation values (in Hounsfield units [HU]) of trabecular bone between the T12 and L5 vertebral levels, with an emphasis on L1 measures (study test); DXA BMD measures (reference standard). Sagittal CT images assessed for moderate-to-severe vertebral fractures. Results: CT-attenuation values were significantly lower at all vertebral levels for patients with DXA-defined osteoporosis (P < 0.001). An L1 CT-attenuation threshold of 160 HU or less was 90% sensitive and a threshold of 110 HU was more than 90% specific for distinguishing osteoporosis from osteopenia and normal BMD. Positive predictive values for osteoporosis were 68% or greater at L1 CT-attenuation thresholds less than 100 HU; negative predictive values were 99% at thresholds greater than 200 HU. Among 119 patients with at least 1 moderate-to-severe vertebral fracture, 62 (52.1%) had nonosteoporotic T-scores (DXA false-negative results), and most (97%) had L1 or mean T12 to L5 vertebral attenuation of 145 HU or less. Similar performance was seen at all vertebral levels. Intravenous contrast did not affect CT performance. Limitation: The potential benefits and costs of using the various CT-attenuation thresholds identified were not formally assessed. Conclusion: Abdominal CT images obtained for other reasons that include the lumbar spine can be used to identify patients with osteoporosis or normal BMD without additional radiation exposure or cost.