Predicting Fracture Risk in Younger Postmenopausal Women: Comparison of the Garvan and FRAX Risk Calculators in the Women’s Health Initiative Study

Background: Guidelines recommend fracture risk assessment in postmenopausal women aged 50–64, but the optimal method is unknown. Objectives: To compare discrimination and calibration of the Fracture Risk Assessment Tool (FRAX) and Garvan fracture risk calculator for predicting fractures in postmenopausal women aged 50–64 at baseline. Design: Prospective observational study. Participants: Sixty-three thousand seven hundred twenty-three postmenopausal women aged 50–64 years participating in the Women’s Health Initiative Observational Study and Clinical Trials. Main Measures: Incident hip fractures and major osteoporotic fractures (MOF) during 10-year follow-up. Calculated FRAX- and Garvan-predicted hip fracture and MOF fracture probabilities. Key Results: The observed 10-year hip fracture probability was 0.3% for women aged 50–54 years (n = 14,768), 0.6% for women aged 55–59 years (n = 22,442), and 1.1% for women aged 60–64 years (n = 25,513). At sensitivity thresholds ≥ 80%, specificity of both tools for detecting incident hip fracture during 10 years of follow-up was low: Garvan 30.6% (95% confidence interval [CI] 30.3–31.0%) and FRAX 43.1% (95% CI 42.7–43.5%). At maximal area under the receiver operating characteristic curve (AUC(c), 0.58 for Garvan, 0.65 for FRAX), sensitivity was 16.0% (95% CI 12.7–19.4%) for Garvan and 59.2% (95% CI 54.7–63.7%) for FRAX. At AUC(c) values, sensitivity was lower in African American and Hispanic women than among white women and lower in women aged 50–54 than those 60–64 years old. Observed hip fracture probabilities were similar to FRAX-predicted probabilities but greater than Garvan-predicted probabilities. At AUC(c) values (0.56 for both tools), sensitivity for identifying MOF was also low (range 26.7–46.8%). At AUC(c) values (0.55 for both tools), sensitivity for identifying any clinical fracture ranged from 18.1 to 34.0%. Conclusions: In postmenopausal women aged 50–64 years, the FRAX and Garvan fracture risk calculator discriminate poorly between women who do and do not experience fracture during 10-year follow-up. There is no useful threshold for either tool.