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Bone mineral density test
Definition
A bone mineral density (BMD) test measures how much calcium and other types of minerals are in an area of your bone.
This test helps your health care provider detect osteoporosis and predict your risk of bone fractures.
Alternative Names
BMD test; Bone density test; Bone densitometry; DEXA scan; DXA; Dual-energy x-ray absorptiometry; p-DEXA
How the Test is Performed
Bone density testing can be done several different ways.
The most common and accurate way uses a dual-energy x-ray absorptiometry (DEXA) scan. It uses low-dose x-rays. (You receive more radiation with a chest x-ray.)
There are two different types of DEXA scans:
- Central DEXA. You lay on a soft table, and the scanner passes over your lower spine and hip. Usually, you do not need to undress. This scan is the best test to predict your risk of fractures.
- Peripheral DEXA (p-DEXA). These smaller machines measure the bone density in your wrist, fingers, leg, or heel. These machines are in doctor's offices, pharmacies, shopping centers, and at health fairs.
How to Prepare for the Test
If you are or could be pregnant, tell your health care provider before this test is done.
How the Test Will Feel
The scan is painless. You will need to remain still during the test.
Why the Test is Performed
Bone mineral density (BMD) tests are used to:
- Diagnose bone loss and osteoporosis
- See how well osteoporosis medicine is working
- Predict your risk of future bone fractures
You should have bone mineral testing or screening if you have an increased risk of osteoporosis. You are more likely to get osteoporosis if you are:
- A woman over 65
- A man over age 70
Women under age 65 and men ages 50 - 70 are at increased risk of osteoporosis if they have:
- A broken bone caused by normal activities, such as a fall from standing height or lower (fragility fracture)
- Chronic rheumatoid arthritis, chronic kidney disease, eating disorders
- Early menopause (either from natural causes or surgery)
- History of hormone treatment for prostate cancer or breast cancer
- Significant loss of height due to compression fractures of the back
- Smoking
- Strong family history of osteoporosis
- Taking corticosteroid medications (prednisone, methylprednisolone) every day for more than 3 months
- Three or more drinks of alcohol per day on most days
Normal Results
The results of your test are usually reported as a T-score and Z-score.
- T-score compares your bone density with that of healthy young women.
- Z-score compares your bone density with that of other people of your age, gender, and race.
With either score, a negative number means you have thinner bones than the standard. The more negative the number, the higher your risk of a bone fracture.
A T-score is within the normal range if it is -1.0 or above.
What Abnormal Results Mean
Bone mineral density testing does not diagnose fractures. Along with other risk factors you may have, it helps predict your risk of having a bone fracture in the future. Your doctor will help you understand the results.
- T-score between -1 and -2.5 indicates the beginning of bone loss (osteopenia).
- T-score below -2.5 indicates osteoporosis.
Treatment recommendation depends on your total fracture risk. This risk can be calculated using the FRAX score. Your health care provider can tell you more about this. You can also find information about FRAX online.
Risks
Bone mineral density uses a slight amount of radiation. Most doctors feel that the risk is very low compared with the benefits of finding osteoporosis before you break a bone.
Considerations
Simple bone density scans using portable machines are often available as part at health fairs or screenings. These portable scanners check the bone density at your wrist or heel. Keep in mind that hip and spine scans are more reliable.
If you are diagnosed with osteopenia or osteoporosis:
- Keep your bones strong by doing regular weight-bearing exercise such as brisk walking, tennis, or yard work.
- Exercise such as tai chi improves balance and reduces risk of falls.
- Check your home for fall hazards, such as loose rugs, to help reduce the risk of falls and fractures.
References
Lim LS, Hoeksema LJ, Sherin K; ACPM Prevention Practice Committee. Screening for osteoporosis in the adult U.S. population: ACPM position statement on preventive practice. Am J Prev Med. 2009;36:366-375.
National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2008.
U.S. Preventive Services Task Force. Screening for osteoporosis: recommendation statement. Am Fam Physician. 2011 May 15;83(10):1197-200.
Reviewed By: Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.
