Bone Density Testing:
What's Involved and Who Should Be Tested

If your health care professional thinks you either have or may be at increased risk for developing osteoporosis, she or he will most likely order a bone density test as part of your diagnostic work-up. This test will measure the amount of calcium and other minerals in your bones; in other words, just how dense and strong your bones are. Bone density testing can detect osteoporosis even before you have fractured a bone, and predict your chances of fracturing a bone in the future. If you have already been diagnosed with osteoporosis, a bone density test every one to two years can be very helpful in monitoring your rate of bone loss or your response to bone-building treatment.

The most accurate bone density test for osteoporosis is dual energy x-ray absorptiometry, known as a DXA scan. It is considered the "gold standard", is widely available, quick, painless, and relatively inexpensive ($150-$300). The DXA usually takes density measurements in your hip or spine because these are the sites where fractures generally occur. Also, the bone that makes up the hip and spine isn't as dense as other bones in the body, so a scan of the hip or spine gives the clinician a more accurate picture of your risk for fracture.

The National Osteoporosis Foundation recommends bone density testing for women:

The DXA scan is an easy and noninvasive test. You can eat, drink and take any medications up until the test, although if you normally take calcium supplements you will be asked not to do so for at least 24 hours before the test. If you had a contrast dye injection (used in some radiological studies such as CT scans) recently, you will have to wait 10 to 14 days before having a DXA scan. Also, before scheduling a DXA scan, be sure to tell your health care professional if you are pregnant because the test emits a very small amount of radiation which may be harmful to your fetus.

For the DXA scan, you may wear loosely fitting clothing or a hospital gown. You will be asked to remove any metal jewelry, buckles or zippers and then you will be positioned on your back on a padded scanning table. For a DXA of the lumbar spine, a padded wedge will be placed under your knees to keep your spine flat, and for a scan of the hip, you will lie flat on your back with your legs straight. The DXA scan, which takes between 10 and 30 minutes is performed by a physician or trained technician. The imager (a mechanical arm-like device) passes slowly over your body without touching it. As the scanner passes over your body, images are projected onto a computer monitor; the computer then analyzes the images and calculates bone density by subtracting the amount of radiation absorbed by soft tissue from that absorbed by bone.

Your DXA scan will be interpreted by a radiologist, who will then give the results, usually within a few days, to your health care professional. The information gathered from your DXA scan will show if your bone density is within normal range or whether it is below normal, putting you at increased risk for a fracture. It will also help your health care professional plan your bone health regimen.

You may have heard about peripheral-DXA, or p-DXA. This scan uses the same technology as the full DXA, but measures density of bones located away from the center of the body, such as your finger, heel and wrist. The p-DXA is faster and simpler than a full DXA, but not as accurate. Placing your finger, hand or foot into a small, light-weight device gives results within a few minutes.

However, keep in mind that DXA scanning is not the only factor in making a diagnosis of osteoporosis. Diagnosis is also based on a full medical assessment which includes your medical history and osteoporosis risk-factor profile.

References