A DEXA scan, also known as a bone mineral density scan, is a useful, easy, and inexpensive imaging test that measures bone density. DEXA stands for “dual-energy X-ray absorptiometry,” and uses very low levels of x-rays. It provides useful details about bone loss, and the risk for osteoporosis and bone fractures. Who should get one, and when?
Osteoporosis literally means “porous bone.” Brittle bones lead to a higher risk of having a bone fracture. As we age, our bones lose thickness and strength; they get weaker and break more easily. Osteoporosis results when we lose bone faster than our body can create new bone tissue. It is seen most often in postmenopausal women, and some don’t realize that they have osteoporosis until after a bone breaks.
How does the DEXA scan work? You will lie on a special x-ray table, and be carefully positioned. As the arm of the DEXA machine passes over the body, it uses two different x-ray beams, which emit very low levels of radiation. The scanner translates bone density measurement data into pictures and graphs. Bone appears white, and fat and muscle appear as shadows in the background.
The DEXA scan comes up with a bone score. The convention is that normal bone is equal to that of a typical 30-year-old woman, with an assigned score of 0. The range of normal bone is from 0 to -1.0. A score between -1.0 and -2.5 is labeled as osteopenia, meaning that the bone mass is low. Many people, including those who are slender and active, fall into this category. Osteopenia will not necessarily progress to osteoporosis. However, if there are other risk factors for fracture, such a person might still be a candidate for an osteoporosis medication. Finally, a score of -2.5 or more is considered to be osteoporosis.
DEXA scans are also used to track bone health and to monitor responses to treatment. They can be used to evaluate body composition, such as the proportion of fat to muscle mass.
Who should get a DEXA scan? Typically, scanning is performed on women, and, depending on risk factors, may begin for some after age 50. Risk factors include a history of broken bones, long-term steroid use, a family history of osteoporosis, the use of certain cancer drugs, and the use of organ transplant medications. Those with rheumatoid arthritis, lupus, diabetes, or liver and kidney disease may be at a higher risk of developing osteoporosis. Petite, thin women with fair complexions are at higher risk, as are smokers and those who consume high levels of caffeine. Even without other risk factors, the U.S. Preventive Services Task Force recommends DEXA scans for all women who are 65 and older.
Subject to the presence of these risk factors, Medicare may cover DEXA scans every two years, with private insurance companies usually following suit. You and your physician can consider all of these risk factors when deciding whether to have a DEXA scan.
If a DEXA scan leads to a diagnosis of osteopenia or osteoporosis, your doctor may suggest treatments including weight-bearing exercise, calcium and vitamin D supplements, and a variety of prescription medications.