FRAX® tool, the WHO algorithm to predict osteoporotic fractures: the first analysis of its discriminative and predictive ability in the Spanish FRIDEX cohort

Abstract

BackgroundThe WHO has recently published the FRAX® tool to determine the absolute risk of osteoporotic fracture at 10 years. This tool has not yet been validated in Spain.Methods/designA prospective observational study was undertaken in women in the FRIDEX cohort (Barcelona) not receiving bone active drugs at baseline. Baseline measurements: known risk factors including those of FRAX® and a DXA. Follow up data on self-reported incident major fractures (hip, spine, humerus and wrist) and verified against patient records. The calculation of absolute risk of major fracture and hip fracture was by FRAX® website. This work follows the guidelines of the STROBE initiative for cohort studies. The discriminative capacity of FRAX® was analyzed by the Area Under Curve (AUC), Receiver Operating Characteristics (ROC) and the Hosmer-Lemeshow goodness-of-fit test. The predictive capacity was determined using the ratio of observed fractures/expected fractures by FRAX® (ObsFx/ExpFx).ResultsThe study subjects were 770 women from 40 to 90 years of age in the FRIDEX cohort. The mean age was 56.8 ± 8 years. The fractures were determined by structured telephone questionnaire and subsequent testing in medical records at 10 years. Sixty-five (8.4%) women presented major fractures (17 hip fractures). Women with fractures were older, had more previous fractures, more cases of rheumatoid arthritis and also more osteoporosis on the baseline DXA. The AUC ROC of FRAX® for major fracture without bone mineral density (BMD) was 0.693 (CI 95%; 0.622-0.763), with T-score of femoral neck (FN) 0.716 (CI 95%; 0.646-0.786), being 0.888 (CI 95%; 0.824-0.952) and 0.849 (CI 95%; 0.737-0.962), respectively for hip fracture. In the model with BMD alone was 0.661 (CI 95%; 0.583-0.739) and 0.779 (CI 95%; 0.631-0.929). In the model with age alone was 0.668 (CI 95%; 0.603-0.733) and 0.882 (CI 95%; 0.832-0.936). In both cases there are not significant differences against FRAX® model. The overall predictive value for major fracture by ObsFx/ExpFx ratio was 2.4 and 2.8 for hip fracture without BMD. With BMD was 2.2 and 2.3 respectively. Sensitivity of the four was always less than 50%. The Hosmer-Lemeshow test showed a good correlation only after calibration with ObsFx/ExpFx ratio.ConclusionsThe current version of FRAX® for Spanish women without BMD analzsed by the AUC ROC demonstrate a poor discriminative capacity to predict major fractures but a good discriminative capacity for hip fractures. Its predictive capacity does not adjust well because leading to underdiagnosis for both predictions major and hip fractures. Simple models based only on age or BMD alone similarly predicted that more complex FRAX® models.

Fracture experience among participants from the FROCAT study: what thresholding is appropriate using the FRAX tool?

“…The ability of the FRAX tool to discriminate between Spanish women with high or low fracture risk shows acceptable values that are similar to studies in other populations [26][27][28] . A more recent refinement led to the construction of a calibrated model to determine three levels of FRAX risk (low, intermediate, high) based on the analysis of the main fracture outcomes of women from the FRIDEX cohort over a 10-year period of follow up 25,26 that better identified women at high risk of fracture (figure 1).…”

“…This observation has been made in prior Spanish female population studies 5,[26][27][28] , and may reflect our slightly younger population, since parental fracture will become more common as an individual (and their parent) ages. Previous fracture shows statistical significance as shown in some studies 22,26 .In previous meta-analysis, smoking has been found to be a risk factor when it comes to fractures. Surprisingly, however, smokers among the female cohort taken from the general Spanish population shows discordant data.…”

“…Surprisingly, however, smokers among the female cohort taken from the general Spanish population shows discordant data. This may be due to the mean age of the cohort, although no significant differences have been found in other Spanish cohort studies 26 .…”

“…This factor has been shown to be a BMD independent risk factor in the available Spanish female data 5,26 and might add to growing evidence that proposes that fall history might be included as a predictor in other osteoporotic fracture scales 29 .…”

“…In addition to what has been said, recent Spanish female population cohort studies have assessed the predictive ability of the FRAX tool locally, and analyzed the FRAX discriminative and predictive ability to predict major osteoporotic fractures 5,[25][26][27][28] . The ability of the FRAX tool to discriminate between Spanish women with high or low fracture risk shows acceptable values that are similar to studies in other populations [26][27][28] .…”