By Anthony L. Komaroff, M.D.

DEAR DOCTOR K:

I just turned 65. At my last medical visit, my doctor said she'd like me to get a bone density test. What is it, and what's involved?

DEAR READER:

A bone density test uses specialized X-rays to measure the thickness and strength of your bones. It is also called bone densitometry or a DXA scan.

Why measure the thickness of your bones? Adults, particularly women, begin to lose bone thickness around age 50. Thinner bones put you at greater risk for fracture. Besides being painful at the time, fractures (particularly hip fractures) can affect your ability to do the things you want to do.

When bones are somewhat thin, the condition is called osteopenia. When bones become very thin, the condition is called osteoporosis. Bone density tests can measure whether you have osteopenia or osteoporosis.

If you're already being treated for osteoporosis, repeated bone density tests can measure the effectiveness of your treatment.

Many authorities recommend routine bone density tests in women aged 65 or older. Early detection is important because exercise and various treatments can help prevent and even reverse bone loss.

So what's involved? During the test, you'll lie on a table. A radiologist or X-ray technician will move a scanner above your spine, hip or wrist. The test measures your bone thickness in these three different parts of the body. Unfortunately, fractures of the spine, hip and wrist are all much more common in people with thin bones.

The test takes 10 to 20 minutes. The test itself is painless, but you may experience some discomfort because you have to lie still on a hard surface.

The test doesn't have any significant risks. You'll be exposed to about one-tenth the amount of radiation as in a single chest X-ray.

You'll get the results within a few days. The diagnosis of osteopenia or osteoporosis is based on your so-called T-score. If you have a T-score that is between minus 1.0 and minus 2.5, you have osteopenia. If it is below minus 2.5, you have osteoporosis.

In general, the lower your bone density, the higher your risk of breaking a bone. Fortunately, treatment options exist. Several different types of medicines protect your bones from getting thinner. Some even help build back up bone that you have lost. Such medicines are relatively new. When I was in medical school, we didn't have a way of measuring bone density. And we didn't have medicines proven to prevent or reverse thin bones.

If your test results indicate that your bones are thinning, talk with your doctor about what you can do to reduce your risk of fracture. We have a lot more information on osteoporosis in our Special Health Report called "Osteoporosis: A Guide to Prevention and Treatment." You can find out more about it at my website.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

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