FRAX tool, the WHO algorithm to predict osteoporotic fractures: the first analysis of its discriminative and predictive ability in the Spanish FRIDEX cohort
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Date
2012
Authors
Azagra, Rafael
Roca, Genís
Encabo, Gloria
Aguyé, Amada
Zwart, Marta
Güell, Sílvia
Puchol, Núria
Gene, Emili
Casado, Enrique
Sancho, Pilar
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Abstract
Background: The 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/design: A 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).
Results: The 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.
Conclusions: The 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.
Citation
Journal or Serie
BMC Musculoskeletal Disorders, 2012, vol. 13, núm. 204