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Bone Densitometry (DXA)
A bone density test determines if you have osteoporosis — a disease that causes bones to become more fragile and more likely to break.
In the past, osteoporosis could be detected only after you broke a bone. By that time, however, your bones could be quite weak. A bone density test makes it possible to know your risk of breaking bones before the fact.
A bone density test uses X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone. The bones that are most commonly tested are located in the spine, hip and forearm.
Why It's Done
Although osteoporosis is more common in older women, men also can develop the condition. Regardless of your sex or age, your doctor may recommend a bone density test if you've:
- Lost height. People who have lost at least 1.6 inches (4 centimeters) in height may have compression fractures in their spines, for which osteoporosis is one of the main causes.
- Fractured a bone. Fragility fractures occur when a bone becomes so fragile that it breaks much more easily than expected. A strong cough or sneeze can sometimes cause fragility fractures.
- Taken certain drugs. Long-term use of steroid medications, such as prednisone, interferes with the bone-rebuilding process, which can lead to osteoporosis.
- Received a transplant. People who have received an organ or bone marrow transplant are at higher risk of osteoporosis, partly because anti-rejection drugs also interfere with the bone-rebuilding process.
- Had a drop in hormone levels. In addition to the natural drop in hormones that occurs after menopause, women's estrogen may also drop during certain cancer treatments. Some treatments for prostate cancer reduce testosterone levels in men. Lowered sex hormone levels weaken bone.
Preparation for Test
Food and medications
Avoid taking calcium supplements for at least 24 hours before your bone density test.
Clothing and personal items
Wear loose, comfortable clothing and avoid wearing clothes with zippers, belts or buttons. Remove all metal objects from your pockets, such as keys, money clips or change.
During your exam, you'll lie on a padded platform while a mechanical arm passes over your body. The amount of radiation you're exposed to is low — much less than the amount emitted during a chest X-ray. The test may take up to 30 minutes to complete.
ResultsA doctor specially trained to interpret a bone density test will analyze the images from your scan and report the findings to your primary care provider.