In the non-HRT arms of the DOPS study, 10-year fracture risk was higher at each level of T score than predicted by the Kanis algorithm. Under-reporting of fractures in registers and inclusion of HRT users are probable explanations for inappropriately low fracture risk estimates for younger women.
Introduction: International recommendations highlight the importance of absolute fracture risk in establishing intervention thresholds. The available estimates of long-term risk have been derived by combining relative risks from meta-analyses with U.S. normative BMD data and Swedish fracture incidence records. We validated the 2001 Kanis risk algorithm using incident fractures observed in untreated women in the first 10 years of the Danish Osteoporosis Prevention Study (DOPS). Comparisons were also made with the relative risks derived from a recent meta-analysis of 12 cohort studies.
Materials and methods: We analyzed DXA of the spine and hip from 872 women who were enrolled in the non-hormone replacement therapy (HRT) arms of the study and had not received HRT, bisphosphonates, or raloxifene. We collected verified reports of fractures at each visit. We focused on fractures of the hip, spine, shoulder, and forearm to provide risks comparable with the Kanis algorithm. Accordingly, asymptomatic radiographic vertebral fractures were not included.
Results: Seventy-eight women (9%) sustained relevant fractures. The risk of fracture increased by 1.32 (95% CI, 1.02; 1.70) for each unit decrease in femoral neck T score and by 1.30 (95% CI, 1.06; 1.58) for each unit decrease in lumbar spine T score at baseline. Absolute fracture risk was higher than expected from the Kanis algorithm at all T score levels. The difference was greatest for participants in the higher range of T scores. At T = -1, the observed risk was 10.9% as opposed to an expected risk of 5.7%. Relative risk gradients were similar to those of the recent meta-analysis.
Conclusions: In healthy women, examined in the first year or two after menopause, 10-year fracture risk was higher at each level of BMD T score than expected from the model by Kanis et al. Inclusion of HRT users in the cohorts used may have led to higher BMD values and lower absolute fracture risk in the Kanis model. These longitudinal data can be used directly in estimating absolute fracture risk in untreated north European women from BMD at menopause.