Probability of fractures predicted by FRAX® and observed incidence in the Spanish ECOSAP Study cohort

Purpose: To assess the ability of the Spanish version of the WHO fracture risk assessment tool (FRAX (R)) to predict the observed incident fractures in the ECOSAP Study cohort. Methods: 5201 women, aged 65 or older, were enrolled in a three-year, prospective study by a non-randomized sampling of consecutive cases in 58 primary care centers in Spain. Participants completed an osteoporosis and fracture risk questionnaire and attended follow-up visits every 6 months. All radiologically or surgically confirmed low-trauma, non-spinal fractures were collected. The individual 10-year absolute risks of hip and major osteoporotic fractures were calculated with the FRAX (R) algorithms for Spain without the inclusion of the bone mineral density (BMD) measurements. Calibration was evaluated by comparing the three-year estimated (E) fractures predicted with FRAX (R) with the number of observed (O) fractures, and their discriminative ability for the probability of new fractures with the area under the receiving operating characteristic (ROC) curves. Results: Fifty (0.96%) women sustained an incident hip fracture, and 201 (3.81%) women presented with major osteoporotic fractures (hip, forearm or humerus). The E/O ratios for hip and major osteoporotic fractures were 1.10 and 0.66 respectively. Clinical vertebral fractures were not collected; therefore, the E/O ratio for major fractures should be expected to be lower. The difference between E and O cases reached statistical significance (chi(2), p<0.001). Areas under the ROC curves were 0.640 and 0.615 for hip and major osteoporotic fractures respectively. Conclusions: The Spanish FRAX (R) underestimates the risk for major osteoporotic fractures. The estimated risk for hip fractures was similar to the observed fractures: however the algorithm had only modest discriminative ability. These results should be interpreted in the context of the relatively low number of observed fractures, especially at the hip. (C) 2011 Elsevier Inc. All rights reserved.