Osteoporosis: Diagnosis with lateral and posteroanterior dual x-ray absorptiometry compared with quantitative CT

PURPOSE: To compare the diagnostic sensitivity of posteroanterior and lateral dual x-ray absorptiometry (PA-DXA, L-DXA, respectively) and quantitative computed tomography (CT). MATERIALS AND METHODS: Among 108 women undergoing lumbar spine bone mineral density assessment, 66 were healthy (mean age, 52.9 years ± 1.2 [standard error of mean]) and 42 had osteoporosis (mean age, 66.9 years ± 1.2). RESULTS: Although both L-DXA and PA-DXA correlated well with quantitative CT (r = .73 and .72, respectively; P <.0001), L-DXA correlated better than PA-DXA with age (r = -.69 and -.50, respectively; P <.0001). Women with osteoporosis showed higher bone loss with quantitative CT (1.33% per year) and L-DXA (0.3% per year) than with PA- DXA (0.07% per year). Logistic regression analysis indicated that quantitative CT and L-DXA but not PA-DXA are significant predictors of osteoporotic fractures. Receiver-operating-characteristic curve analyses showed L-DXA to have a sensitivity and specificity closer to those of quantitative CT than did PA-DXA. CONCLUSION: Performance of L-DXA helped discriminate better than PA-DXA between healthy subjects and those with osteoporosis.