Dual Energy X-ray Absorptiometry Overview

This is a test that measures the density (or thickness) of your bones.

The DEXA scan is an x-ray scan that uses a small amount of radiation to take pictures of different bones. These pictures are used to measure the density of the bones at the spine, hip, wrist, and sometimes other sites, such as a finger or the heel bone. Measurements of the spine and hip are called central DXA. Those done on the arms or legs are called peripheral DXA. In some cases, your doctor may order a whole body scan.

Prior to Test

• Eat normally on the day of the test.

• If you have had a barium study, or have been injected with contrast dye for a CT scan or MRI , wait at least seven days before having a DEXA scan.

• Wear loose, comfortable clothing. Do not wear clothing with metal zippers, belts, or buttons.

Description of Test

Total Body Measurement

You will lie on a table. A machine will pass over your body and take measurements of your bone density by sending a thin, invisible beam of low-dose x-rays through your bones. The amount of radiation is very small, less than 1/10 the dose of a standard chest x-ray . A picture of your skeleton will be made based on how much the x-rays have changed after passing through your bones.

Spine or Hip Measurement

Your toes will be placed in a “pigeon-toed” position, and the same steps above are done.

Wrist Measurement

You will sit in a chair beside the DEXA machine. Your arm will be placed in a holding device while the measurement is taken.

After Test

You will be able to leave after the test is done.

How Long Will It Take?

About 10 minutes

Will It Hurt?

No

The test results are usually available within a few days. Your test results will show two types of scores:

• T score—This number shows the amount of bone you have in comparison to a young adult of the same gender with peak bone mass. A score above -1 is considered normal. A score between -1 and -2.5 may mean you have osteopenia, the first stage of bone loss. A score below -2.5 means you may have osteoporosis.
• Z score—This number shows the amount of bone you have in comparison to other people of your age group, gender, and size.

These test results will help your doctor determine your risk for bone fractures.

RESOURCES:

The American Academy of Orthopaedic Surgeons
http://www.aaos.org/

National Osteoporosis Foundation
http://www.nof.org/

CANADIAN RESOURCES:

Health Canada
http://www.hc-sc.gc.ca/index-eng.php/

Osteoporosis Canada
http://www.osteoporosis.ca/english/home/default.asp?s=1/

References:

Sartoris D, Dalinka MK, Alazraki N. Osteoporosis and bone mass measurement. Radiology. 2000;215(suppl):397-414.

Osteoporosis: bone density tests. Am Acad Orthop Surg Bull. 1999;47(3).

National Osteoporosis Foundation website. Available at: http://www.nof.org/ . Accessed October 14, 2005.