## WHO T-Score Classification for Bone Density **Key Point:** The T-score is the number of standard deviations (SD) a patient's bone mineral density (BMD) differs from the mean BMD of a healthy 30-year-old adult of the same sex. It is the gold standard for diagnosing osteoporosis. ### WHO Classification Table | Category | T-Score Range | Clinical Significance | |----------|---------------|----------------------| | Normal | ≥ −1.0 | No bone loss | | Osteopenia | −1.0 to −2.5 | Mild bone loss; increased fracture risk | | **Osteoporosis** | **≤ −2.5** | Significant bone loss; high fracture risk | | Severe osteoporosis | ≤ −2.5 + fragility fracture | Established osteoporosis with fracture | **High-Yield:** A T-score of **−2.5 or lower** is the diagnostic threshold for osteoporosis. This threshold was chosen because it corresponds to a 2.5-fold increase in fracture risk compared to healthy young adults. ### Important Notes - T-scores are used for **postmenopausal women and men ≥50 years old** - Z-scores (comparison to age-matched controls) are used for **premenopausal women and men <50 years old** - The diagnosis is made at the **lowest T-score site** (hip, spine, or forearm) - A single T-score ≤ −2.5 is sufficient for diagnosis; no fracture is required **Mnemonic:** **NOOT** = **N**ormal (≥−1), **O**steopenia (−1 to −2.5), **O**steoporosis (−2.5 to −3.5), **T**errible/Severe (≤−3.5). **Clinical Pearl:** The presence of a fragility fracture (e.g., hip, vertebra, wrist) in a patient with T-score between −1 and −2.5 (osteopenia) warrants treatment as if osteoporosis is present. [cite:Park 26e Ch 3] 
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