A bone mineral density (BMD) test measures the
density of minerals (such as
calcium) in your bones using a special
computed tomography (CT) scan. This information is used to estimate the
strength of your bones.
We all lose some bone mass as we age.
Bones naturally become thinner (called
osteopenia) as you grow older, because existing bone is
broken down faster than new bone is made. As this occurs, our bones lose
calcium and other minerals and become lighter, less dense, and more porous.
This makes the bones weaker and increases the chance that they might break
With further bone loss,
osteopenia leads to
osteoporosis. So the thicker your bones are, the
longer it takes to get osteoporosis. Although osteoporosis can occur in men, it
is most common in women older than age 65.
If your bone density is
lower than normal, you can take steps to increase your bone strength and reduce
your chances of having a fracture. Some ways to increase bone density and
strength include combining calcium and vitamin D supplements with
weight-bearing exercise (such as walking), weight training (such as lifting
weights or using weight machines), and using medicines.
There are several different ways to measure
Ultrasound is a screening test that is
sometimes offered at events such as health fairs. It is only used to look for problems. If results from an ultrasound test find
low bone density, DEXA is recommended to confirm the results. Ultrasound uses
sound waves to measure BMD, usually in your heel. Ultrasound is quick,
painless, and does not use potentially harmful radiation like X-rays. One
disadvantage of ultrasound is it can't measure the density of the bones most
likely to fracture from osteoporosis (the hip and spine). Ultrasound is not used to
keep track of how well medicine for osteoporosis is working.
Before being screened for osteoporosis, you may want to
think about what you will do if the tests show that you have a high chance of
Health Tools help you make wise health decisions or take action to improve your health.
A bone mineral density (BMD) test is
Avoid wearing clothes with metal buttons
or buckles for the test. You also may want to remove any jewelry that might
interfere with the scan, such as a bracelet if you are having the scan done on
A bone mineral density (BMD) scan is usually
done in the special radiology department or clinic by a technologist.
Peripheral dual-energy X-ray absorptiometry (P-DEXA) machines are portable
units that can be used in a doctor's office.
You will need to lie
on your back on a padded table. You can usually leave your clothes on. You may
need to lie with your legs straight or with your lower legs resting on a
platform built into the table.
The machine will scan your bones
and measure the amount of radiation they absorb. The DEXA technique, which
scans the hip and lower spine, takes about 20 minutes to perform. Other
techniques may take 30 to 45 minutes.
Portable machines (P-DEXA)
can measure bone density in the wrist or forearm.
Testing at least two different bones
(preferably the hip and spine) each time is the most reliable way of measuring
BMD. It is best to test the same bones and to use the same measurement
technique and BMD equipment each time.
A bone mineral density test does not cause
pain. If you have back pain, it may be uncomfortable to lie still on a table
during the scan.
During a bone mineral density (BMD) scan, you are
exposed to a very low dose of radiation. A BMD scan is not recommended for
pregnant women because of the radiation exposure to the unborn baby.
A bone mineral density (BMD) test measures
the density of minerals (such as
calcium) in your bones using a special
computed tomography (CT) scan. Results are usually available in 2 to 3
Results of bone mineral density tests can be reported in
Your T-score is your BMD compared to the
average score of a healthy 30-year-old. It is expressed as a standard deviation
(SD), which is a statistical measure of how closely each person in a group is
to the average (mean) of the group. The average BMD is determined by measuring
the bone density of a large group of healthy 30-year-olds (young adult
reference range). BMD values are then reported as a standard deviation from the
mean of this reference group. Almost all 30-year-old people have a BMD value
within 2 standard deviations of this mean.
The following table contains the World Health
Organization's definitions of osteoporosis based on
bone mineral density T-scores.
Less than 1 standard deviation (SD) below the young
adult reference range (more than –1)
1 to 2.5 SDs below the young adult reference range (–1
More than 2.5 SDs below the young adult reference range
(–2.5 or less)
If your bone mineral density test
result is low:
Low BMD values may be caused by other problems,
Your BMD value may also be compared to
other people of your age, sex, and race. This is called your Z-score. It is
given in standard deviations (SD) from the average value for your age
Reasons you may not be able to
have the bone mineral density (BMD) test or why the results may not be helpful include:
CitationsU.S. Preventive Services Task Force (2011). Screening for Osteoporosis: Recommendation Statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf10/osteoporosis/osteors.htm.Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Other Works ConsultedChernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Liu H, et al. (2008). Screening for osteoporosis in men: A systematic review for an American College of Physicians guideline. Annals of Internal Medicine, 148(9): 685–701.Nayak, S, et al. (2006). Meta-analysis: Accuracy of quantitative ultrasound for identifying patients with osteoporosis. Annals of Internal Medicine, 144 (11): 832–841.Qaseem A, et al. (2008). Screening for osteoporosis in men: A clinical practice guideline from the American College of Physicians. Annals of Internal Medicine, 148(9): 680–684. Also available online: http://www.acponline.org/clinical_information/guidelines/guidelines.U.S. Preventive Services Task Force (2011). Screening for Osteoporosis: Recommendation Statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf10/osteoporosis/osteors.htm.
August 30, 2012
Anne C. Poinier, MD - Internal Medicine & Carla J. Herman, MD, MPH - Geriatric Medicine
To learn more visit Healthwise.org
© 1995-2012 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.