27th February 2025

Defining osteoporosis

Osteoporosis is characterised by decreased bone mineral density (BMD) and micro-architectural tissue changes that increase bone fragility and, therefore, risk of fractures (particularly affecting the hip, spine and wrists). The WHO defines osteoporosis as a BMD (assessed via DXA, dual-energy x-ray absorptiometry, scan) ≥2.5 standard deviations below the mean for young, healthy adults of the same sex and ethnicity (i.e., a T-score of -2.5), with the pre-disease state of osteopenia defined as a T-score between 1 and 2.5 standard deviations below normal.

Where there is no clear cause, patients are diagnosed with idiopathic osteoporosis. Though the term idiopathic suggests an unidentified aetiology, the underlying pathogenesis relates to age-related changes ± polygenic variants. Where suspected, fracture risk should be assessed in anyone over 50 with a known risk factor, all women over 65 and men over 75. Risk factors include but are not limited to previous fragility fracture, advanced age, female sex, early menopause, low body weight (BMI <18.5 kg/m²), family history of osteoporosis, frequent or current use of systemic glucocorticoids, smoking, and excessive alcohol intake (≥14 units/week).