Bone Density Scan

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 the test. Avoid wearing metal jewelry or clothes with metal parts such as buttons or buckles.

For a central DEXA scan: You lie on your back on a padded table. The scanning arm passes over your hips and spine while another passes under you. You must stay still and may be asked to hold your breath. The test takes 10 to 30 minutes, with results in a few days. For a peripheral DEXA (p-DEXA) scan: You place a finger, hand, forearm, or foot in a portable device. It takes a few minutes, and results are available shortly.

The bone density scan uses very low doses of radiation and is safe for most people. However, it is not recommended during pregnancy because even low radiation could harm a developing baby.

Understanding results

Results are usually given as T-scores and Z-scores. A higher number means greater bone density; the lower the score, the higher the risk of fracture. T-scores are used for postmenopausal women and men age 50 or older. Z-scores are used for premenopausal women, men under 50, and children. The T-score results may show one of the following:

• Normal bone density: Bone density is within the expected range for a healthy young adult. Limitation: This result does not rule out future bone loss or fracture risk due to other factors. Next step: Maintain healthy habits: regular exercise, adequate calcium and vitamin D intake. Repeat scanning may be recommended every 10 to 15 years for low fracture risk.
• Osteopenia (low bone mass): Bone density is lower than normal (T-score between -1.0 and -2.4), indicating increased risk for developing osteoporosis. Limitation: This is a risk category, not a disease diagnosis. The test may be less accurate if you have spinal surgery, deformity, fractures, or arthritis. Next step: Your provider will recommend steps to prevent further bone loss including exercise, adding calcium and vitamin D to your diet, and possibly prescription medicines. Repeat central DEXA scan every 2-5 years depending on fracture risk.
• Osteoporosis (probably): A T-score of -2.5 or less. This means you probably have osteoporosis, a disease that makes bones very thin and brittle. Limitation: The result says 'probably' because clinical context and other tests may be needed to confirm. DEXA scans may be less accurate with spinal surgery, deformity, fractures, or arthritis. Next step: Your provider will recommend treatments to increase bone density and reduce fracture risk, such as medications, exercise, and dietary changes. Repeat central DEXA scan every 2 years is typically recommended.

• 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

If your results show low bone density (osteopenia) or osteoporosis, your provider will recommend steps to prevent further bone loss: getting more exercise (walking, dancing, weight machines), adding calcium and vitamin D to your diet, and possibly taking prescription medicines. Your provider may suggest repeat scans based on your fracture risk: every 2 years for high risk, every 3-5 years for moderate risk, and every 10-15 years for low risk. Additional tests (calcium blood test, vitamin D test, hormone tests) may be ordered to confirm a diagnosis or monitor treatment.

• 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

U.S. National Library of Medicine: Bone Density Scan