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Osteoporosis Health Center

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Bone Density

How It Is Done continued...

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 DXA 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-DXA) 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 bone density. It is best to test the same bones and to use the same measurement technique and bone density equipment each time.

How It Feels

A bone density test does not cause pain. If you have back pain, it may be uncomfortable to lie still on a table during the scan.


During a bone density scan, you are exposed to a very low dose of radiation. A bone density scan is not recommended for pregnant women because of the radiation exposure to the unborn baby.


A bone density test measures the density of minerals (such as calcium) in your bones using a special X-ray. Results are usually available in 2 to 3 days.

Results of bone density tests can be reported in several ways.


Your T-score is your bone density compared to the average score of a healthy 30-year-old. It is expressed as a standard deviation (SD), which is a statistical measure of how closely each person in a group is to the average (mean) of the group. The average bone density is determined by measuring the bone density of a large group of healthy 30-year-olds (young adult reference range). Bone density values are then reported as a standard deviation from the mean of this reference group. Almost all 30-year-old people have a bone density value within 2 standard deviations of this mean.

  • A negative (-) value means that you have thinner bones (lower bone density) than an average 30-year-old. The more negative the number is, the less bone density you have compared with an average 30-year-old.
  • A positive (+) value means that your bones are thicker and stronger than an average 30-year-old.

WebMD Medical Reference from Healthwise

Last Updated: November 14, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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