T-Score Calculator — Bone Density DXA Assessment

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How this is calculated

A DXA (dual-energy X-ray absorptiometry) scan measures bone mineral density in grams per square centimetre (g/cm²) at one or more skeletal sites, most commonly the femoral neck (hip), lumbar spine (L1–L4) or total hip. The T-Score expresses how far your measured density lies from the average peak bone mass of a healthy young adult of the same sex. It is the number of standard deviations above (positive) or below (negative) that young-adult reference mean. The reference values built into this calculator are approximate NHANES III young-adult peak BMD figures by site and sex (Looker et al., 1995, Journal of Bone and Mineral Research); your scanner's own manufacturer reference database may differ slightly.

The WHO diagnostic thresholds for postmenopausal women and older men are: T-Score at or above −1.0 is normal; between −1.0 and −2.5 is osteopenia (low bone mass); and at or below −2.5 meets the WHO definition of osteoporosis. The lowest T-Score across all measured sites is typically used for the clinical diagnosis. Note that the lumbar spine score in older adults can be artificially elevated by vertebral osteophytes or aortic calcification, and the femoral neck is the site validated for the FRAX fracture-risk algorithm.

T-Scores are designed for postmenopausal women and men aged 50 and over. For premenopausal women, younger men and children, Z-Scores (comparing to an age- and sex-matched reference population) are more appropriate and this calculator should not be used for those groups. A T-Score is one input into a broader clinical assessment — always discuss results with a clinician who can account for risk factors, medication history and clinical context.