The importance of absolute bone mineral density in the assessment of antiresorptive agents used for the prevention of osteoporotic fractures.

The usefulness of bone mineral density (BMD) monitoring during antiresorptive treatment is still controversial. This study aimed to determine which factors of change (absolute value or the percent change from the baseline) in BMD are associated with the risk of future fractures. A total of 565 postmenopausal osteoporosis who were treated antiresorptive drugs were included in this prospective observational study. Lumbar BMD (LBMD) was measured at baseline and 1-yr after the initial and subsequent incident fracture was observed. The percent changes in LBMD at 1 yr were 5.4 ± 6.4% and 118 (20.9%) achieved increased LBMD with change of classification to >-2.5 standard deviation (SD). After the initial 1-yr examination, incident fractures developed in 152 (26.9%). The incident fracture risk was significantly associated with the absolute value in LBMD, but not with the percent change. A Cox proportional hazard model demonstrated that increased LBMD with change of classification to >-2.5 SD was a significant predictor for a reduction in incident fractures (hazard ratio: 0.41, 95% confidence interval: 0.21-0.71). In conclusion, these results suggest that monitoring of the antifracture efficacy of antiresorptive treatments should be based on the absolute value of BMD. In particular, increased change to >-2.5 SD is important for reducing the future fracture risk.