A bone density test uses special X-rays to measure how many grams of calcium and other bone minerals — collectively known as bone mineral content — are packed into a segment of bone. The higher your mineral content, the denser your bones are. And the denser your bones, the stronger they generally are and the less likely they are to break. Doctors use a bone density test to determine if you have, or are at risk of, osteoporosis.
Bone density tests are not the same as bone scans. Bone scans require an injection beforehand and are usually used to detect fractures, cancer, infections and other abnormalities in the bone.
The U.S. Preventive Services Task Force recommends routine bone density screening if:
- You're a woman age 65 or older
- You're 60 and at increased risk of osteoporosis
The older you get, the higher your risk of osteoporosis because your bones become weaker as you age. Your race also makes a difference. You're at greatest risk of osteoporosis if you're white or of Southeast Asian descent. Black and Hispanic men and women have a lower, but still significant risk. Other risk factors for osteoporosis include low body weight, a personal history of fractures, a family history of osteoporosis and using certain medications that can cause bone loss.
Research hasn't yet determined the optimal interval for repeat bone density screenings, or the right age to stop screening. However, two or more years may be needed between tests to reliably measure a change in your bone density. Your doctor can recommend the best screening interval for you based on your personal medical history and osteoporosis risk factors.
How do you prepare for a bone density test?
Bone density tests are easy, fast and painless. Virtually no preparation is needed. In fact, some simple versions of the bone density tests can be done at your local pharmacy or drugstore. If you're having the test done, be sure to tell your doctor beforehand if you've had recent oral contrast or nuclear medicine tests. These tests require an injection of radioactive tracers that might interfere with your bone density test.
How is a bone density test done?
Bone density tests are usually done on bones that are most likely to break because of osteoporosis. These sites include the lumbar vertebrae, which are in the lower region of your spine, the narrow neck of your femur bone adjoining the hip, and the bones of your wrist and forearm.
The equipment for bone density tests includes large machines on which you can lie down (central devices) as well as smaller, portable machines that measure bone density on the periphery of your skeleton, such as in your finger, wrist or heel (peripheral devices).
Dual energy X-ray absorptiometry (DEXA) scans measure the bone density at your hip or spine(Our facility measures both areas). This test offers very precise results and is the preferred test for diagnosing osteoporosis. During this test, you lie on a padded platform for a few minutes while an imager — a mechanical arm-like device — passes over your body. It won't touch you. The test does, however, emit radiation, though your exposure during a bone density test is commonly about one-tenth of the amount emitted during a chest X-ray. This test usually takes five to 10 minutes to complete.