DEXA scan
Meaning of DEXA scan: Ordered when fracture risk is in question, the test takes minutes, needs no injection, and uses a very small radiation dose.
Definition of DEXA scan
A DEXA scan is a short, low-dose x-ray test that measures bone mineral density, usually at the hip and lower spine. The person lies still on a padded table while a scanning arm passes overhead. Nothing is injected and no preparation is needed beyond removing metal objects from clothing. Results are reported as standardized scores rather than as raw density figures.
What happens during the scan?
The person lies on their back on an open table, fully clothed, with a positioning block placed under the legs to flatten the lower spine. A scanning arm travels slowly above the body while a detector beneath records how much of each x-ray beam gets through. There is no tunnel, no injection and no contrast agent, and the machine does not touch the skin. Radiation exposure is very small, well below that of many routine x-ray examinations. The main practical requirement is holding still, since movement blurs the measurement in the same way it blurs a photograph. Recent tests using barium or a radioactive tracer can interfere with the reading, which is why the order of appointments sometimes matters.
How is it different from a bone scan?
| DEXA scan | Bone scan | |
|---|---|---|
| What it measures | How much mineral the bone contains | How active bone turnover is at each site |
| How | Two x-ray beams from outside the body | A radioactive tracer given by injection |
| Usual question | Is bone density low, and is it changing | Is there a fracture, infection or spread of cancer to bone |
The names sound interchangeable and the tests are not. Confusing the two is a common source of misunderstanding about what has actually been ordered.
What is the result used for?
Density at the hip and spine is one of the strongest available predictors of future fracture, so the result feeds into an overall assessment of risk alongside age, previous fractures, family history and medication use. It is the standard measurement for identifying osteoporosis and the intermediate band often called low bone mass. Repeat scans track change over time, though bone changes slowly, so tests spaced too closely together mostly measure the machine's own variation rather than the person's. Comparing scans performed on different machines is unreliable for the same reason.
Also known as
Used in a sentence
A DEXA scan was ordered to assess bone density following the patient's fragility fracture.
Good to know
A DEXA scan result is reported as standardized scores rather than raw density, and repeat scans are most comparable when performed on the same machine, since differences between scanners can be larger than genuine change in bone.