OBJECTIVE: To evaluate the diagnostic accuracy of computed tomography (CT) for detecting osteoporosis in Brazilian adults, using dual-energy X-ray absorptiometry (DXA) as the reference standard.
MATERIALS AND METHODS: We conducted a retrospective analysis of adults over 50 years of age who underwent CT (chest, abdominal, or lumbar scans) and DXA within a 60-day interval, between January 2012 and December 2022. Vertebral bone attenuation at L1 was quantified in Hounsfield units. Thresholds of > 160 HU and < 100 HU were used in order to classify bone as normal and osteoporotic, respectively. Two musculoskeletal radiologists, working independently, performed subjective classifications. Sensitivity, specificity, predictive values, and interobserver agreement (Cohen’s kappa) were calculated. The influence of contrast use and scanner heterogeneity was considered.
RESULTS: Ninety-five patients met the inclusion criteria. On the basis of the DXA results, we identified 39 normal cases, 46 cases of osteopenia, and 10 cases of osteoporosis. For detecting normal bone, objective CT measurements demonstrated a sensitivity of 88.6% and a specificity of 95.5%. For detecting osteoporosis, the sensitivity was 75.3% and the specificity was 99.7%. For the subjective classification, the level of interobserver agreement was fair (κappa = 0.384). The study included CT scans from different scanner models, with and without contrast enhancement.
CONCLUSION: Opportunistic CT demonstrated high specificity but only moderate sensitivity for osteoporosis detection. The attenuation thresholds previously validated in populations elsewhere show promise for use in Brazil. However, scanner variability, contrast use, and limited sample size constrain generalizability. Larger, multicenter prospective studies are warranted.

Keywords: Bone density; Osteoporosis/diagnostic imaging; Prevalence; Absorptiometry, photon; Tomography, X-ray computed.