Bone Density Scan
Reviewed
Also called: Bone mineral density test, BMD test, DEXA scan, DXA scan, Bone densitometry, Dual-energy x-ray absorptiometry scan
A bone density scan, also known as a DEXA or DXA scan, is a low-dose x-ray that measures calcium and other minerals in your bones.
Specimen: N/A (imaging)
Why this test may be ordered
- Diagnose osteopenia (low bone mass)
- Diagnose osteoporosis
- Predict your risk of future fractures
- See if treatment for osteoporosis is working
- Screen for bone loss in women age 65 or older or in individuals with risk factors such as very low body weight, fractures after age 50, height loss, family history, or medical conditions like diabetes or rheumatoid arthritis
Preparation and collection
You may be told to stop taking calcium supplements 24 to 48 hours before your test. You should also avoid wearing metal jewelry or clothes with metal parts, such as buttons or buckles.
The most common and accurate method is with dual-energy x-ray absorptiometry, also known as a central DEXA scan. The scan checks the bone density of your lower spine, hip, wrist, or entire body. While the machines are scanning, you need to stay very still. The test usually takes 10 to 30 minutes.
A bone density scan uses very low doses of radiation. It is safe for most people. But it is not recommended during pregnancy. Even low doses of radiation could harm a developing baby. Be sure to tell your provider if you are pregnant or think you may be pregnant.
Understanding results
Bone density results are often given as T-scores and Z-scores. A higher number means that you have greater bone density. The lower your score, the higher your risk of bone fracture.
- T-score of -1.0 or higher: A T-score of -1.0 or higher. This is considered normal bone density. Limitation: DEXA scans are not as accurate if you have a history of spinal surgery or spinal deformity, fractures, or arthritis in your spine. Next step: The recommendations are to get a central DEXA scan every two years for high risk, every 3 to 5 years for moderate risk, and every 10 to 15 years for low risk.
- T-score between -1.0 and -2.4 (osteopenia): This means you have low bone density (osteopenia) and may be at risk for developing osteoporosis. Limitation: DEXA scans are not as accurate if you have a history of spinal surgery or spinal deformity, fractures, or arthritis in your spine. Next step: If your results show you have low bone density, your provider will recommend steps to prevent further bone loss.
- T-score of -2.5 or less (osteoporosis): A T-score of -2.5 or less. This means you probably have osteoporosis. Limitation: DEXA scans are not as accurate if you have a history of spinal surgery or spinal deformity, fractures, or arthritis in your spine. Next step: But your provider may order more tests to confirm a diagnosis or to find out if bone loss treatment is working.
- The test uses low-dose radiation; it is not recommended during pregnancy.
- Central DEXA scans may be less accurate if you have a history of spinal surgery, spinal deformity, fractures, or arthritis in your spine.
- Peripheral DEXA (p-DEXA) scans provide good information about fracture risk but cannot give as much detail as a central DEXA scan.
- Results labeled as osteopenia or osteoporosis are based on statistical comparisons and may not fully capture individual fracture risk; clinical follow-up is necessary.
- The test does not measure bone quality or other factors affecting bone strength.
What to do next
Your provider may recommend how often you need to have repeat scans, based on your risk of bone fractures. If you have questions about your results and/or treatments for bone loss, talk to your provider.
- Who should get a bone density scan?
- How should I prepare for a bone density scan?
- What do T-scores and Z-scores mean?
- How often should I repeat the scan?
- Are there other tests that might be needed?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.