Bone mineral density in lower thoracic vertebral for osteoporosis diagnosis in older adults during CT lung cancer screening

Quantitative computed tomography (QCT) has been used to diagnose osteoporosis. Whether the thresholds of lumbar bone mineral density (LBMD) are applicable to the thoracic spine should be validated. This study explored the value of lower thoracic BMD (TBMD) in diagnosing osteoporosis in older adults during CT lung cancer screening. This study included 610 subjects who underwent QCT scans with both LBMD and TBMD. Osteoporosis was diagnosed based on LBMD using the ACR criteria (gold standard). Receiver operating characteristic (ROC) curve was used to define the TBMD thresholds. TBMD was translated into LBMD (TTBMD) and osteoporosis was defined based on TTBMD using ACR criteria. The performance of TBMD thresholds and TTBMD in identifying osteoporosis was determined using the Kappa test. In addition, 227 subjects with baseline TBMD data and followed up spine fracture were included to show the association between TBMD- and TTBMD-based osteoporosis and fracture. The performance of TBMD in identifying osteoporosis was low (kappa = 0.66) if using the ACR criteria. Two thresholds of TBMD for identifying osteopenia (128 mg/cm 3 ) and in identifying osteoporosis (91 mg/cm 3 ) were obtained with areas under the curve of 0.97 and 0.99, respectively. The performance of the identification of osteoporosis/osteopenia using the two thresholds or TTBMD both had good agreement with the gold standard (kappa = 0.78, 0.86). Osteopenia and osteoporosis identified using the thresholds (adjusted hazard ratio (HR) = 4.43, 95% confidence interval (CI): 1.31–15.06; adjusted HR = 18.72, 95% CI: 5.13–68.36) or TTBMD (adjusted HR = 2.78, 95% CI: 1.16–6.72; adjusted HR = 10.28, 95% CI: 4.22–25.08) were also associated with fractures. Calculating the threshold of TBMD or normalizing TBMD to LBMD both showed good performance in identifying osteoporosis in older adults during CT lung cancer screening.