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. You may find these machines in doctor's offices, pharmacies, shopping centers, and 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 for osteoporosis. You are more likely to get osteoporosis if you are:

  • A women over 65
  • A man over age 70

Women under age 65 and men ages 50 - 70 are at increased risk for osteoporosis if they have:

  • A broken bone caused by normal activities, such as a fall from standing height or less ("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 (See: 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 Values

The results of your test are usually reported as a "T score" and "Z score."

  • The T score compares your bone density with that of healthy young women.
  • The Z score compares your bone density with that of other people of your age, gender, and race.

In 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. However, 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.

  • A T score between -1 and -2.5 indicates the beginning of bone loss (osteopenia).
  • A T score below -2.5 indicates osteoporosis.

Treatment recommendations depend on your total fracture risk.

What the risks are

Bone mineral density uses a little bit of radiation. But most experts feel that the risk is very low compared with the benefits of spotting osteoporosis before you break a bone.

Special considerations

Simple bone density scans using portable machines may be available as part of health fairs or screenings. These portable scanners may check the density of your wrist or heel. However, keep in mind that hip and spine scans are more reliable.

Figures

References

U.S. Preventive Services Task Force. Screening for osteoporosis: recommendation statement. Am Fam Physician. 2011 May 15;83(10):1197-200.

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, D.C.: National Osteoporosis Foundation; 2008.

Nelson HD, Haney EM, Dana T, Bougatsos C, Chou R. Screening for osteoporosis: an update for the U.S. Preventive Services Task Force. Ann Intern Med. 2010;153:99-111.

Revision

Last reviewed 11/7/2011 by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc., 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.

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