What analytic method should clinicians use to derive spine T-scores and predict incident fractures in men? Results from the MrOS study

Summary: In this study, the area under the curve was highest when using the lowest vertebral body T-score to diagnose osteoporosis. In men for whom hip imaging is not possible, the lowest vertebral body T-score improves the ability to diagnose osteoporosis in men who are likely to have an incident fragility fracture. Introduction: Spine T-scores have limited ability to predict fragility fracture. We hypothesized that using lowest vertebral body T-score to diagnose osteoporosis would better predict fracture. Methods: Among men enrolled in the Osteoporotic Fractures in Men Study, we identified cases with incident clinical fracture (n=484) and controls without fracture (n=1,516). We analyzed the lumbar spine bone mineral density (BMD) in cases and controls (n=2,000) to record the L1-L4 (referent), the lowest vertebral body, and International Society for Clinical Densitometry (ISCD)-determined T-scores using a male normative database and the L1-L4 T-score using a female normative database. We compared the ability of method to diagnose osteoporosis and, therefore, to predict incident clinical fragility fracture, using area under the receiver operator curves (AUCs) and the net reclassification index (NCI) as measures of diagnostic accuracy. ISCD-determined T-scores were determined in only 60 % of participants (n=1,205). Results: Among 1,205 men, the AUC to predict incident clinical fracture was 0.546 for L1-L4 male, 0.542 for the L1-L4 female, 0.585 for lowest vertebral body, and 0.559 for ISCD-determined T-score. The lowest vertebral body AUC was the only method significantly different from the referent method (p=0.002). Likewise, a diagnosis of osteoporosis based on the lowest vertebral body T-score demonstrated a significantly better net reclassification index (NRI) than the referent method (net NRI +0.077, p=0.005). By contrast, the net NRI for other methods of analysis did not differ from the referent method. Conclusion: Our study suggests that in men, the lowest vertebral body T-score is an acceptable method by which to estimate fracture risk.