## Investigation of Choice for Osteoporosis Diagnosis **Key Point:** DXA scan is the gold standard for diagnosing osteoporosis and predicting fracture risk in both postmenopausal women and older men. ### Why DXA is the Gold Standard 1. **Precision and accuracy** — Measures bone mineral density (BMD) at clinically relevant sites (lumbar spine, femoral neck, forearm) 2. **T-score calculation** — Enables standardized diagnosis: - Normal: T-score ≥ −1.0 - Osteopenia: T-score between −1.0 and −2.5 - Osteoporosis: T-score ≤ −2.5 3. **Fracture risk assessment** — FRAX algorithm integrates DXA results with clinical risk factors 4. **Low radiation dose** — Effective dose ~3 µSv (lower than chest X-ray) 5. **Reproducibility** — Excellent precision for serial monitoring during treatment **High-Yield:** DXA is recommended for all postmenopausal women ≥65 years and men ≥70 years, and for younger individuals with risk factors [cite:Park 26e Ch 3]. ### Comparison with Other Investigations | Investigation | Sensitivity | Specificity | Clinical Use | Limitations | |---|---|---|---|---| | **DXA** | High | High | Gold standard for diagnosis & monitoring | Cannot assess bone quality | | QCT | Moderate | High | Research, specific sites (hip, spine) | Higher radiation, expensive | | Biochemical markers | Variable | Variable | Assess bone turnover, predict response | Not diagnostic; high variability | | pQUS | Moderate | Moderate | Screening in resource-limited settings | Cannot diagnose; poor monitoring | **Clinical Pearl:** In this postmenopausal woman with clinical features of osteoporosis (kyphosis, height loss, vertebral wedging), DXA confirms diagnosis and provides baseline for treatment monitoring. ### FRAX Integration DXA T-score at femoral neck feeds into FRAX to calculate 10-year probability of: - Major osteoporotic fracture - Hip fracture This guides treatment decisions (e.g., when to start bisphosphonates). 
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