DEXA Scan Assesses Bone Density and Osteoporosis Risk
A DEXA scan (dual energy x-ray absorptiometry) is a test that assesses whether you have normal bone density, low bone density (also referred to as osteopenia), or osteoporosis. Typically, a DEXA scan, also referred to as a central DEXA scan, measures your bone density at the hip or spine which is where most osteoporosis-related fractures occur. If you are unable to have the hip or spine tested (e.g., perhaps due to hip replacement), then the radius bone of the forearm is substituted as the site for the test.
What Is It Like to Have a DEXA Scan?
A DEXA scan is painless and does not take a lot of time. As you lie on your back on an imaging table, a mechanical device (the scanner) passes over your body to assess the hip and spine regions. The DEXA scan emits a very low level of radiation, about one-tenth of the radiation that you get with a chest x-ray. The test takes approximately 10 to 15 minutes.
Who Should Get a DEXA Scan?
The National Osteoporosis Foundation recommends DEXA scans for:
- women 65 years and older
- men 70 years and older
- people who have had a broken bone after age 50
- women of menopausal age with risk factors for osteoporosis
- post-menopausal women under age 65 with risk factors for osteoporosis
- men 50-69 with risk factors for osteoporosis
A DEXA scan is also recommended if you have had spine x-rays showing a break or bone loss, back pain that may be related to spine fracture, or height loss (one half-inch or more within a year or 1-1/2 inches from total height).
What Does a DEXA Scan Show?
A DEXA scan detects weak or brittle bones before you have a fracture. The score helps to predict your chance of fracture in the future, and perhaps the need for osteoporosis medication. The DEXA scan, when compared to previous DEXA scan results, indicates whether your bone density is improving, worsening, or staying the same.
It helps determine if your osteoporosis medication is working. After a fracture occurs, a DEXA scan can assess if it was likely due to osteoporosis.
Interpreting DEXA Scan Results
DEXA scan results are reported as T-scores. A T-score indicates how much higher or lower your bone density is than that of a healthy, 30-year-old adult. The World Health Organization states that a:
- T-score of -1.0 or above is normal
- T-score that falls between -1.0 and -2.5 indicates low bone density, or osteopenia
- T-score of -2.5 or below confirms a diagnosis of osteoporosis
Essentially, lower T-scores correlate with lower bone density. Your T-score is just one tool for evaluating whether you need to take osteoporosis medications or make lifestyle modifications which may improve your score. Other risk factors are considered as well.
There is also a Z-score. A Z-score compares your bone density to what is expected for someone of your age, gender, weight, ethnicity, and race.
Other Types of Bone Density Tests
You may have come across peripheral tests or screening tests for osteoporosis. These are typically offered at health fairs. There is the pDEXA (peripheral dual energy x-ray absorptiometry), QUS (quantitative ultrasound), and the pQCT (peripheral quantitative computed tomography).
It is important to know that the screening tests are not able to diagnose osteoporosis. Screening tests simply identify people who should obtain further testing with a central DEXA. The results of a peripheral versus a central DEXA test are also not comparable.