Osteoporosis Health Center

How It Feels

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

Risks

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

Results

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

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

T-score

Your T-score is your BMD 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 BMD is determined by measuring the bone density of a large group of healthy 30-year-olds (young adult reference range). BMD values are then reported as a standard deviation from the mean of this reference group. Almost all 30-year-old people have a BMD value within 2 standard deviations of this mean.

• A negative (-) value indicates 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 indicates that your bones are thicker and stronger than an average 30-year-old.

The following table contains the World Health Organization's definitions of osteoporosis based on bone mineral density T-scores.

If your bone mineral density test result is low:

• You may have osteoporosis. Doctors usually use the lowest T-score to diagnose osteoporosis. For example, if your T-score at your spine is -3 and your T-score at your hip is -2, the spine T-score would be used to diagnosis osteoporosis.
• You have a higher-than-average chance of breaking a bone. The more negative your T-score, the greater your chances of breaking a bone during a fall or from a minor injury. Every change of 1 SD means a twofold increase in the risk of fracture at that site. For example, if you have a T-score of -1, your chances of having a broken bone are 2 times greater than if your T-score was 0.