Bone Density Test

What is a bone density test?

A bone density test is a way to see if your bones are healthy and strong. The test measures the density and strength of your bones.

This test is different from a bone scan, which looks for fractures or areas of bone inflammation.

Why is this test done?

A bone density test checks the health of your bones. It may be done for several possible reasons:

• It may be recommended for women if:
  • They are 65.
  • They are 60 and have an increased risk for osteoporosis (for example, because they smoke or don’t get regular exercise).
  • They have a bone fracture after menopause.
• It may be recommended for men if:
  • They have a family history of osteoporosis.
  • They take a medicine that weakens the bones.
  • They have other risk factors.
  • There is evidence that their bones are weak (they have had unusual or frequent fractures, for example).

Your bones naturally get less solid as you get older. This loss of density weakens the bones, and weaker bones put you at higher risk for fractures, such as a spine fracture or broken hip. If your bones are somewhat less dense than normal, you have osteopenia. If your bones have lost a lot of density, you have osteoporosis.

Each year there are approximately 700,000 spine fractures and 250,000 hip fractures in the US. Most of these fractures happen in people who have osteoporosis. To help prevent fractures, it is important to diagnose osteoporosis. Osteoporosis can then be treated with diet, exercise, and sometimes medicine to help make the bones strong again.

Bone density tests are much more sensitive than normal X-rays. Normal X-rays do not detect bone loss until at least 30% of the bone mass has been lost. Bone density tests allow healthcare providers to diagnose weakening bones at an earlier stage. The test helps your healthcare provider decide if you need treatment for osteoporosis.

Your provider will review your risk factors and talk to you about whether a bone density test might be recommended for you.

How do I prepare for this test?

• Don't wear clothing with buttons, snaps, or zippers from the waist down on the day of the test. If you wear pants with an elastic waistband or cloth tie, you won't need to get undressed for the test.
• If you have recently had X-ray tests using barium or any nuclear medicine tests, wait at least a week after those tests before you have a bone density test.
• Tell your healthcare provider if you are or might be pregnant.

How is the test done?

There are several different kinds of bone density tests. Some use sound waves (ultrasound). Others use small amounts of radiation.

A test commonly used to measure bone density with radiation is dual energy X-ray absorptiometry (DXA or DEXA). The test is painless. During the test you lie down on a padded table. It's best not to move while the test is being done, but you can breathe normally. It takes just a few minutes to check the density of your spine and hip. (The hip and spine are the most common areas checked because they are most prone to fracture if your bones are weak.) The amount of radiation used for this test is very low. It is about the same amount you would get on a long plane flight and less than you are exposed to during a typical chest X-ray.

There are other tests besides the DEXA scan. Different tests have different strengths and weaknesses. Talk to your healthcare provider about which test is right for you.

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

The test results are expressed as 2 types of scores:

• The T-score compares your bone mineral density (BMD) to the expected bone density value of a healthy young adult (about age 30) of the same gender and ethnicity.
• The Z-score compares your BMD to the BMD of a healthy person who is about the same age and body size as you.

The T score is uses a statistical measure called a standard deviation (SD). The SD measures the difference between your BMD and that of a healthy young adult (the reference value). Each additional "-1 SD" ("minus 1 standard deviation") equals a 10 to 12% decrease in bone density. The T-score measure is most often used to decide about treatment.

T score results are classified as follows:

T score (SD)         Bone Density Classification
----------------------------------------------------
Above -1           normal
-1 to -2.5         osteopenia (low bone mass)
Below -2.5         osteoporosis (very low bone mass)
----------------------------------------------------

The Z score is used to interpret the test results if you are very young or very old. It is the number of standard deviations (SD) above or below the reference value for your age. This allows a comparison of your test results with the results for women your age.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your overall health, risk factors for osteoporosis, and lifestyle. Your healthcare provider will consider all of these factors before deciding if you need treatment and what the treatment might be. All you may need to do is get more exercise and eat a better diet or take a calcium and vitamin D supplement. Or you may need to take medicine to help strengthen your bones. You may need to repeat the test again in a year or two to see if the health of your bones has changed.

Talk to your healthcare provider about your result and ask questions such as:

• if you need more tests
• what kind of treatment you might need
• when you need to be tested again
• what lifestyle, diet, or other changes you might need to make