## WHO Classification of Bone Mineral Density **Key Point:** The WHO diagnostic classification uses T-score thresholds derived from DEXA scanning to categorize bone health status. T-score is the number of standard deviations (SD) the patient's BMD differs from the mean BMD of a healthy 30-year-old reference population. ### WHO T-Score Classification | Category | T-Score Range | Clinical Significance | Fracture Risk | |----------|---------------|----------------------|---------------| | Normal | ≥ −1.0 | Healthy bone density | Low | | Osteopenia | −1.0 to −2.5 | Low bone mass; intermediate risk | Moderate | | Osteoporosis | ≤ −2.5 | Significantly reduced BMD | High | | Severe Osteoporosis | ≤ −2.5 + fragility fracture | Established disease with fracture | Very high | **High-Yield:** The threshold of −2.5 SD was chosen because it represents the fracture risk equivalent to that of a 50-year-old white woman (the reference population used by WHO). This single cutoff applies to all ages and both sexes for diagnostic purposes. **Clinical Pearl:** - Osteopenia (−1.0 to −2.5) does NOT automatically require treatment; treatment decisions depend on FRAX score and absolute fracture risk. - A patient with T-score ≤ −2.5 AND a history of fragility fracture is classified as **severe osteoporosis** and requires immediate treatment. - T-score interpretation is most reliable at the lumbar spine, femoral neck, and total hip; forearm and heel are less commonly used. **Mnemonic:** **"−2.5 is the fix"** — T-score ≤ −2.5 defines osteoporosis and typically triggers treatment consideration. [cite:Park 26e Ch 3] 
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