Diagnostic Imaging

How does a bone density test work?

A Answers (3)

  • AMichael Roizen, MD, Internal Medicine, answered

    Bone density tests work by giving a measure of a bone’s mineral content. The dual-energy x-ray absorptiometry (DXA) scan is the most common bone density test. It passes a beam of x-rays through a large bone, usually the spine or hip. The x-rays blocked by dense bone are different from those blocked by soft tissue. Based on the amount blocked by dense bone compared to soft tissue, you can figure out how dense your bones are.


    Another common bone density test is the ultrasound. This method bounces sound waves over bone (typically, in your heel) to see if it bounces off. The only down side to this test is that you can’t use this method to assess the spine or hip, the most troubling spots for osteoporosis, or to monitor the effectiveness of osteoporosis treatments.
  • AHealthwise answered

    A bone mineral density (BMD) scan is usually done in the special radiology department or clinic by a technologist. Peripheral dual-energy X-ray absorptiometry (P-DEXA) machines are portable units that can be used in a doctor's office.

    You will need to lie on your back on a padded table. You can usually leave your clothes on. You may need to lie with your legs straight or with your lower legs resting on a platform built into the table.

    The machine will scan your bones and measure the amount of radiation they absorb. The DEXA technique, which scans the hip and lower spine, takes about 20 minutes to perform. Other techniques may take 30 to 45 minutes.

    Portable machines (P-DEXA) can measure bone density in the wrist or forearm.

    Testing at least two different bones (preferably the hip and spine) each time is the most reliable way of measuring BMD. It is best to test the same bones and to use the same measurement technique and BMD equipment each time.

    This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. To learn more visit

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  • AHarris McIlwain, MD, Rheumatology, answered
    A bone-density test shows whether the bones are thinner than normal and cannot withstand the same amount of stress as they could in earlier years. So if a test shows low bone density, your risk for fractures and osteoporosis increases. Increasing your bone density lowers your risk for osteoporosis. This is a risk factor that can be treated and controlled.
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How can bone mineral density (BMD) be determined?