bone mineral density (BMD) test

Alternative Names

BMD test; Bone density test

Definition

A bone mineral density (BMD) test can help your health care provider confirm a diagnosis of osteoporosis. The test can help in several ways:

• BMD testing is one of the most accurate ways to assess your bone health.
• When repeated over time, it can be used to monitor your rate of bone loss.
• It can detect osteoporosis at its earliest stage, so treatment can begin sooner.
• If you are being treated for osteoporosis, BMD testing can help your health care provider monitor your response to the treatment.

How the test is performed

Several different kinds of machines can do BMD testing. The most common methods use low-dose X-rays (about one-tenth the radiation dose of a chest X-ray). While you are lying in on a cushioned table, a scanner passes over your body. Typically, the machine takes X-rays of your lower spine and hip. In most cases you won't need to undress.

There are portable machines that just measure the bone density in your wrist or heel, and some experts believe these are useful preliminary screening tools that can help identify people who may have osteoporosis. However, your bone density can differ from site to site within your body, so these machines may not give a true picture of your risk of a hip fracture.

How to prepare for the test

Remove any jewelry before the BMD test. Inform your health care provider if you may be pregnant.

How the test will feel

The scan is painless, although you will need to remain still during the test.

Why the test is performed

Your health care provider may request a BMD test to confirm a diagnosis of osteoporosis.

Normal Values

The results of your test are usually reported as a "T score" and "Z score."

• The T score compares your bone density with that of healthy young women.
• The Z score compares your bone density with that of other people of your age, gender, and race.

In either score, a negative number means you have thinner bones than the standard. The more negative the number, the thinner your bones. A T score is within the normal range if it is a positive number, or at least no more negative than -1.0. (For example, -0.5 is within the normal range, although it is getting borderline.)

Your doctor will help you understand the results.

What abnormal results mean

• A T score from -1 to -2.5 indicates the beginning of bone loss (osteopenia).
• A T score below -2.5 indicates osteoporosis.

What the risks are

BMD testing involves exposure to a low level of radiation. Most experts feel that the risk is very low compared with the benefits of identifying osteoporosis before you break a bone.

Special considerations

Regular BMD testing can be important in combating osteoporosis in certain people. The overall cost-benefit value of screening everyone, including those who are not at high risk, is still a matter of debate. Many insurance companies today will pay for bone density testing under certain circumstances.

Most experts agree women over age 65 years are at highest risk and should have bone density tests.

Woman under 65 with additional risk factors for osteoporosis may also be screened.

Simple bone density scans using portable machines may be available as part of health fairs or screenings. These portable scanners may check the density of your wrist or heel. However, keep in mind that hip and spine scans are more reliable.