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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.
BMD test; Bone density test; Bone densitometry; DEXA scan; DXA; Dual-energy x-ray absorptiometry; p-DEXA; Osteoporosis - BMD
Bone density testing can be done in several 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:
If you are or could be pregnant, tell your provider before this test is done.
DO NOT take calcium supplements for 24 hours before the test.
You'll be told to remove all metal items from your body, such as jewelry and buckles.
The scan is painless. You need to remain still during the test.
Bone mineral density (BMD) tests are used to:
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:
Women under age 65 and men ages 50 to 70 are at increased risk of osteoporosis if they:
Current practice recommends BMD retesting every 2 years. However, some women may be able to wait a much longer time between their screening tests. Talk to your provider about how often you should be tested.
The results of your test are usually reported as a T-score and Z-score:
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.
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 provider will help you understand the results.
If your T-score is:
Treatment recommendation depends on your total fracture risk. This risk can be calculated using the FRAX score. Your provider can tell you more about this. You can also find information about FRAX online.
Bone mineral density uses a slight amount of radiation. Most experts feel that the risk is very low compared with the benefits of finding osteoporosis before you break a bone.
Berry SD, Samelson EJ, Pencina MJ, et al. Repeat bone mineral density screening and prediction of hip and major osteoporotic fracture. JAMA. 2013;310(12):1256-1262. PMID: 24065012 www.ncbi.nlm.nih.gov/pubmed/24065012.
Chernecky CC, Berger BJ. Bone densitometry (dual-energy x-ray absorptiometry, DXA, DEXA scan) - diagnostic. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:239-241.
Committee on Practice Bulletins-Gynecology, The American College of Obstetricians and Gynecologists. ACOG Practice Bulletin N. 129. Osteoporosis. Obstet Gynecol. 2012;120(3):718-734. PMID: 22914492 www.ncbi.nlm.nih.gov/pubmed/22914492.
De Paula FJA, Black DM, Rosen CJ. Osteoporosis and bone biology. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 13th ed. Philadelphia, PA: Elsevier; 2016:chap 29.
National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation. Updated November 11, 2015.
U.S. Preventive Services Task Force. Screening for osteoporosis: recommendation statement. Am Fam Physician. 2011;83(10):1197-1200. PMID: 21568254 www.ncbi.nlm.nih.gov/pubmed/21568254.