Densitometry is a method of measuring bone mineral density. Its task is to detect osteopenia and osteoporosis in time and to assess fracture risk before the bone breaks.
The "gold standard" of densitometry is dual-energy X-ray absorptiometry, or DXA (DEXA). There are other methods (quantitative CT, ultrasound densitometry), but it is by DXA that the WHO diagnostic criteria are formulated.
How it is done and what is measured
Most often a central DXA is done — the lumbar spine and the proximal femur (the femoral neck) are scanned; peripheral densitometry assesses the forearm, heel or fingers. The patient lies clothed, the exam is painless and takes a few minutes.
The radiation dose is very small — less than an ordinary chest X-ray. Hip density best predicts future fractures, so special importance is given to measuring it.
The T-score and the Z-score
The T-score compares your bone density with the peak density in young healthy people and is used in postmenopausal women and men from age 50 — it is by this score that the diagnosis is made under the WHO classification.
The Z-score compares density with peers of the same sex and age; it is used in young people, children and premenopausal women. A low Z-score is a signal to look for secondary causes of bone loss.
Who and how often
Screening is recommended for women from age 65, and for younger women with risk factors (early menopause, low weight, a fracture after age 50, taking glucocorticoids, hyperparathyroidism and others). Men are referred for densitometry when they have risk factors.
How often it is repeated depends on the initial result and the risk — usually once every 1–2 years, to track the trend in density and the effect of treatment.
Reference ranges
Interpretation of the densitometry (DXA) T-score by the WHO classification:
| Normal | T ≥ −1.0 |
| Osteopenia | T from −1.0 to −2.5 |
| Osteoporosis | T ≤ −2.5 |
Frequently asked questions
How does densitometry differ from DEXA?
Densitometry is the task itself: to measure bone density. DEXA (dual-energy X-ray absorptiometry) is the specific technology that does it most often and on which the WHO criteria are based. So DEXA is the main type of densitometry.
Is densitometry harmful?
The radiation dose with DXA is very low — less than an ordinary chest X-ray and many times below the annual natural background. The exam is painless and takes a few minutes.