Fracture risk prediction and the decision to treat low bone density

Dr Nicole Opie1, Dr Kathy Zhu2, Professor Bronwyn Stuckey1,2

1Keogh Institute For Medical Research, 2Department of Endocrinology and Diabetes, Sir Charles Gairdner Hospital

Background: Institution of bone preserving therapy in women without a minimal trauma fracture (MTF) depends on prediction of absolute risk of fracture. PBS threshold for subsidy of anti-resorptive medication is age >70 years with bone mineral density (BMD) t-score < -2.5, but not absolute fracture risk.

Aims: To compare the risk of fracture predicted by on-line calculators.

Methods: Garvan and FRAX (Australia) were interrogated for 10 year risk for hip fracture and any fracture for women aged 60 to 85 in 5 year increments, and BMD t-score from +3 to -3. FRAX (China) was interrogated similarly for patients of Asian descent.

Results: Garvan consistently predicted a higher risk of MTF than did FRAX, more so in the prediction of any fracture, than for hip fracture. Discrepancy increased with increasing age and decreasing BMD. Greater discrepancy was found between Garvan and FRAX (China). The PBS subsidy corresponds to a 10 year fracture risk prediction at the hip of 2.9% by FRAX and 5.7% by Garvan, and at any site of 7.8% and 21.0% respectively.

Conclusion: The decision to prescribe anti-resorptive therapy for prevention of osteoporotic fracture may depend on which fracture risk engine is used to calculate absolute fracture risk.