• You should not have had a recent a barium examination or have been injected with a contrast material for a computed tomography (CT) scan or radioisotope scan.
• You may have to wait 10 to 14 days before undergoing a DEXA test. No other preparation is required.

You will be asked to lie on your back on a couch and keep still while an x-ray detector comes over for your test. The x-ray equipment is energised and the detector measures the rays that come through the bone. This information is sent to a computer that calculates a score of the average density of the bone. A low score indicates that the bone is less dense than it should be, some material of the bone has been lost, and is more prone to fracture.

The bones commonly scanned are the vertebrae (backbones), hip and wrist. These are the bones common to fractures due to osteoporosis. The scan is painless and takes 15-20 minutes.

Your test results will be in the form of two scores:

• T score – This number shows the amount of bone you have compared with a young adult of the same gender with peak bone mass. A score above -1 and -2.5 is classified as osteopenia, the first stage of bone loss. A score below -2.5 is defined as osteoporosis. The T score is used to estimate your risk of developing a fracture.
• Z score – This number reflects the amount of bone you have compared with other people in your age group and of the same size and gender. If this score is unusually high or low, it may indicate a need for further medical tests.

Small changes may normally be observed between scans due to differences in positioning and usually are not significant.

BENEFITS

• DEXA bone densitometry is a simple, quick and non-invasive procedure.
• The amount of radiation used is extremely small – less than one-tenth the dose of a standard chest x-ray.
• DEXA bone density testing is the most accurate method available for the diagnosis of osteoporosis and is also considered an accurate estimator of fracture risk.

RISKS

• The effective radiation dose from this procedure is about 0.01 mSv, which is about the same as the average person receives from background radiation in one day.
• Women should always inform the radiographer if there is any possibility that they are pregnant.