DXA bone scan reports

What DXA measures

Dual-energy X-ray absorptiometry (DXA) measures bone mineral density (BMD) - the standard diagnostic test for osteoporosis and osteopenia, typically at the lumbar spine and hip
Widely used for osteoporosis screening in postmenopausal women and older men, and for monitoring treatment response over time

Results are reported as a T-score (comparison to a young healthy adult reference population - used for diagnosis) and a Z-score (comparison to an age/sex-matched population - used to flag unexpectedly low BMD for age, prompting a search for a secondary cause)

T-score interpretation (WHO criteria): >=-1.0 = normal, -1.0 to -2.5 = osteopenia, <=-2.5 = osteoporosis - measured at the lowest of the reported sites (spine, total hip, or femoral neck)
T-score is used for diagnosis in postmenopausal women and men over 50; in younger patients or children, the Z-score is preferred, since the T-score reference population (young healthy adults) is not appropriate for comparison
A Z-score <=-2.0 in any age group is considered "below the expected range for age" and should prompt investigation for a secondary cause (e.g. hyperparathyroidism, hypogonadism, coeliac disease, glucocorticoid excess) rather than assuming primary age-related osteoporosis alone

DXA-defined osteoporosis (T-score <=-2.5) or a prior fragility fracture generally prompts treatment consideration (bisphosphonates or other agents - see osteoporosis drug mechanisms); osteopenia is managed by overall fracture risk assessment (often combined with a tool such as FRAX) rather than BMD alone
Serial DXA (typically at ~2-year intervals) monitors treatment response, though the clinical significance of small BMD changes on serial scans is debated relative to fracture outcome data

Osteoporosis, osteopenia, glucocorticoid-induced osteoporosis, secondary causes of unexpectedly low BMD for age

DXA measures bone quantity, not bone quality - some patients fracture at a T-score above the osteoporosis threshold, and fracture risk assessment tools (incorporating clinical risk factors alongside BMD) provide a more complete picture than the T-score in isolation

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