Bone densitometry scans (general)

Reviewed by Dr Sarah Burnett, consultant radiologist and Dr John Pillinger, GP

What is a bone densitometry scan?

A bone densitometry scan is a special type of X-ray test used to measure the calcium content of the bone, usually in the lumbar region (the lower back) and the hips. The examination is also called a DEXA-scan, QDR-scan or BMD (bone mineral density) measurement.

How does a bone densitometry scan differ from an X-ray?

A bone densitometry scan measures the calcium content in the bones, which cannot be evaluated in an ordinary X-ray. Although an X-ray may appear to show that the bones have a low calcium content, the information is unreliable, so someone with osteoporosis may have perfectly normal X-rays. An X-ray is far more reliable when it comes to detecting a recent bone fracture.

What is a bone densitometry scan used for?

A scan can help a doctor who is examining a patient for osteoporosis to assess their risk of having a bone fracture within the next few years. In general, people with a bone mineral density significantly lower than that normal for their age and sex are more likely to break a bone. If the patient then receives medical treatment, the scan can be repeated after two years to assess their progress.

How is a bone densitometry scan carried out?

The scan will take between 10 and 30 minutes, depending on the equipment used and the parts of the body examined.

If the doctor is checking for osteoporosis, the lumbar spine and the hips are usually examined, as well as the forearm as it will give a different calcium content from other body parts. Patients can eat immediately before the test and remain fully dressed as long as their clothes have no metal buttons or zippers.

Recently portable scanners, which can be used in a GP's surgery and check the BMD of the heel bone (calcaneum), have been growing in popularity.

An example of a left-hip bone scan

The blue areas on the graph show the usual bone mass for women of different ages. As illustrated, the bone mass is lower among elderly women.

A 70-year-old woman's bone mass is indicated by a cross in the figure. It is estimated that 95 per cent of the population belong within the blue areas. Those in the dark blue area have a bone mass above average in relation to age, while people belonging to the light blue area are below average in relation to their age.

The curve for men is similar but is higher placed on the chart and shows a smaller decline with age.

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