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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; Osteoporosis-BMD

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. DEXA uses low-dose x-rays. (You receive more radiation with a chest x-ray.)

There are two types of DEXA scans:

  • Central DEXA. You lie on a soft table. 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 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, age 65 or older
  • A man, age 70 or older 

Women under age 65 and men ages 50 to 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
  • Taking thyroid hormone replacement
  • Three or more drinks of alcohol a day on most days

Current practice recommends BMD retesting every 2 years. However, recent research suggests that some women may be able to wait a much longer time between their screening tests. Discuss with your doctor how often you should be tested.

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 average. 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.

If your T-score is:

  • Between -1 and -2.5, you may have early bone loss (osteopenia).
  • Below -2.5, you likely have 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.

References

National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2013.

U.S. Preventive Services Task Force. Screening for osteoporosis: recommendation statement. Am Fam Physician. 2011;83:1197-200.

Berry SD, Samelson EJ, Pencina MJ, et al. Repeat bone mineral density screening and prediction of hip and major osteoporotic fracture. JAMA. 2013;310:1256-1262.

Committee on Practice Bulletins-Gynecology, The American College of Obstetricians and Gynecologists. ACOG Practice Bulletin 129. Osteoporosis. Obstet Gynecol. 2012;120:718-734.


Review Date: 11/10/2013
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 David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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