DEXA scan

A DEXA scan (dual energy X-ray absorptiometry, also called a bone density scan) measures how much calcium and other minerals your bones hold. It uses a very low dose of X-rays, much lower than a standard X-ray. Most often it measures the hip and lower spine, where weak bones often break. Sometimes the forearm is scanned instead. Smaller scanners that measure the wrist, hand or foot give less detail, and a full hip and spine scan may follow.

Osteoporosis causes no symptoms until a bone breaks. A DEXA scan can show thin bones before that happens, estimate the chance of a break, and check whether a treatment is working. It is offered to people at risk, such as adults over 50, and to younger people with risk factors such as smoking or an earlier broken bone. Other reasons include a fracture after 50, loss of height, very low body weight and a family history of osteoporosis.

Most people need little preparation.

1. You may stay in your clothes or change into a gown. Metal fasteners must be off the area.
2. You lie on your back on a flat, padded table. It is open, with no tunnel.
3. A scanning arm passes slowly over your body, and a detector measures the X-rays that pass through. You lie still and may be asked to hold your breath for a few seconds.
4. When it is over you can get up and go home.

The scan takes about 10 to 30 minutes. A scan of the wrist, hand or foot takes only a few minutes.

You can go back to your normal day. Results are not usually given on the day. They usually come within a few days, and the doctor who asked for the scan explains them. The result is often used together with a fracture risk assessment, which estimates your chance of osteoporosis and of breaking a bone.

The radiation is much lower than in a standard X-ray, and the scan is very safe for most people. It is not recommended in pregnancy, because X-rays can harm an unborn baby, so tell the team if you might be pregnant. The result is less accurate if you have had spine surgery or have a curved spine, fractures or arthritis of the spine.

The result is a T-score, which compares your bones with those of a healthy young adult, or a Z-score for younger people, which compares you with others of your age and sex. A T-score of -1 or higher is considered healthy. Between -1 and -2.5 means low bone density (osteopenia), and -2.5 or lower may mean osteoporosis. Doctors read the score together with your age, earlier fractures and other risk factors.

A DEXA scan cannot show the cause of thin bones. If your bones are thin, you may be advised more exercise, calcium and vitamin D, or medicines, and blood tests may look for a cause. Ask your doctor how soon to repeat the scan.