Comparison of the Osteoporosis Self-Assessment Tool for Asians and the fracture risk assessment tool - FRAX to identify densitometric defined osteoporosis: A discriminatory value analysis in a multi-ethnic female population in Southeast Asia

Objectives: The accuracy of FRAX® as a screening tool to identify osteoporosis and how it compares with tools such as Osteoporosis Self-Assessment Tool for Asians (OSTA), in Southeast Asian women has so far been unexplored. We aimed to determine the FRAX® thresholds that accurately identify densitometric osteoporosis and to compare its performance with that of OSTA for this purpose.

Methods: Singaporean postmenopausal women (n = 1056) were evaluated. FRAX® Major Osteoporotic Fracture Probability (MOFP), Hip Fracture Probability (HFP) scores, and OSTA indices were calculated. Receiver operating characteristic (ROC) curves were constructed and via the Youden index, the optimal cut-off points of balanced sensitivity and specificity for dual energy X-ray absorptiometry (DXA)-defined osteoporosis were identified and the performance characteristics were compared.

Results: A FRAX® MOFP threshold of ≥3.7% had sensitivity, specificity, positive predictive value and negative predictive value of 0.78 (0.73-0.83), 0.63 (0.59-0.66), 0.4 (0.36-0.44), and 0.9 (0.87-0.92), respectively in identifying osteoporosis. The corresponding values for a HFP threshold of ≥0.6% were 0.85 (0.80-0.89), 0.58 (0.55-0.62), 0.39 (0.35-0.43), and 0.92 (0.9-0.94) and that for an OSTA index cut-off of ≤ -1.2 were 0.76 (0.70-0.81), 0.74 (0.71-0.77), 0.48 (0.43-0.54), and 0.91 (0.88-0.93). The area under the ROC curves were 82.8% (79.9%-85.6%), 77.6% (74.2%-81%), and 79.6% (76.5%-82.8%) for OSTA, MOFP, and HFP thresholds respectively.

Conclusions: FRAX® and OSTA perform comparably in identifying osteoporosis in our population. OSTA has only 2 parameters and may be simpler to use. However, FRAX® may also have a role in primary screening to identify the postmenopausal woman to be referred for DXA scanning and may help facilitate fracture risk reduction discussions with the patient.