A DEXA scan is a special type of X-ray that measures bone mineral density (BMD).
DEXA stands for "dual energy X-ray absorptiometry". This type of scan may also be called:
- a DXA scan
- a bone density scan
- a bone densitometry scan
DEXA scans are often used to diagnose or assess someone's risk of osteoporosis, a condition that weakens bones and makes them more likely to break.
As well as being quick and painless, a DEXA scan is more effective than normal X-rays in identifying low bone mineral density.
You may need to have a DEXA scan if you're:
- over 50 years of age with a risk of developing osteoporosis
- under 50 with other risk factors – such as smoking or a previous fracture
The World Health Organization (WHO) has created a 10-year Fracture Risk Assessment Tool, which applies to both men and women between 40 and 90 years of age. The tool can be used to assess if a DEXA scan is appropriate and calculates your risk of fracture in the next 10 years.
Osteoporosis can affect people of both sexes and all ages, although older, post-menopausal women are particularly at risk. This is because after the menopause the level of oestrogen declines, resulting in a decrease in bone mineral density (BMD).
The more dense your bones, the stronger and less likely they are to fracture (break). Osteoporosis doesn't cause any symptoms until a bone is broken.
It used to be difficult to measure bone density and identify those at risk of developing osteoporosis until a fracture occurred. However, it's now possible to measure bone density before someone gets a fracture.
Read more about when DEXA scans are used.
Measuring bone density
During a DEXA scan, X-rays are passed through your body. Some radiation is absorbed by the bone and soft tissue and some travels through your body.
Special detectors in the DEXA scanner measure how much radiation passes through your bones, and this information is sent to a computer.
Your bone density measurements will be compared with the bone density of a young healthy adult or an adult of your own age, gender and ethnicity.
Read more about how DEXA scans are carried out.
DEXA scans use a much lower level of radiation than standard X-ray examinations, which means that the radiographer (the technical specialist carrying out the scan) can stay in the scanning room with you during the scan.
The amount of radiation used during a DEXA scan varies depending on the area of the body being examined, but is very low and less than two days' exposure to natural background radiation (NBR).
By comparison, a chest X-ray uses the equivalent of about three days' exposure to NBR, and a flight to North America is equivalent to approximately a week's exposure to NBR.
Despite being very safe procedures, DEXA scans and X-rays aren't recommended for pregnant women, as X-rays can damage an unborn child.
Read more about your health during pregnancy.