First Time User? Enroll now.
COVID-19: Vaccine information, testing, treatment, and additional resources
Home > Health Library > Bone Density
A bone density test is a kind of X-ray test. It measures the density of minerals (such as calcium) in your bones. This information helps your doctor estimate the strength of your bones.
We all lose some bone mass as we age. Bones naturally become thinner as you grow older. This is because existing bone tissue is broken down faster than new bone is made. As this occurs, our bones lose calcium and other minerals. They also become lighter and less dense. This makes the bones weaker and makes them more likely to break (fracture).
With further bone loss, low bone density (sometimes called osteopenia) can lead 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 increase it and your strength. You can do things like exercising, lifting weights or using weight machines. You can also make sure to get enough calcium and vitamin D. And you may need to take certain medicines.
There are several different ways to measure bone density.
Ultrasound is a screening test that is sometimes offered at events such as health fairs. If results from an ultrasound test find low bone density, DXA is advised to confirm the results. Ultrasound uses sound waves to measure bone density, usually in your heel. It is quick and painless. And it does not use potentially harmful radiation like X-rays. One downside of ultrasound is that it can't measure the density of the bones in the hip and spine. These are the bones most likely to fracture from osteoporosis. Ultrasound is not used to keep track of how well medicine for osteoporosis is working.
Before you are screened for osteoporosis, you may want to think about what you will do if the tests show that you have a high chance of getting osteoporosis.
Health Tools help you make wise health decisions or take action to improve your health.
Doctors may recommend bone density tests for:footnote 1, footnote 2
Avoid wearing clothes with metal buttons or buckles. You also may want to remove any jewelry that might cause a problem with the scan. For instance, don't wear a bracelet if you are having the scan done on your wrist.
In most cases, a bone density scan is done in a radiology department or clinic by a technologist. Peripheral dual-energy X-ray absorptiometry (P-DXA) 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 probably can leave your clothes on. You may need to lie with your legs straight. Or you may lie 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 DXA scan, which scans the hip and lower spine, takes about 20 minutes. Other kinds of scans may take 30 to 45 minutes.
Portable machines (P-DXA) can measure bone density in the wrist or forearm.
Testing at least two different bones each time is the most reliable way of measuring bone density. The hip and spine bones are preferred. It is best to test the same bones each time. The same type of scan and bone density equipment should also be used.
A bone density test does not cause pain. But if you have back pain, it may bother you to lie still on a table during the scan.
During a bone density scan, you are exposed to a very low dose of radiation. A bone density scan is not advised for pregnant women because it exposes the unborn baby to radiation.
A bone density test is a kind of X-ray test. It measures the density of minerals (such as calcium) in your bones. Results are usually ready in 2 to 3 days.
Results of bone density tests can be reported in several ways.
Your T-score is your bone density compared to the average score of a healthy 30-year-old. (This is called the young adult reference range). It is expressed as a standard deviation (SD).
The following table contains the World Health Organization's definitions of osteoporosis based on bone density T-scores.
Less than 1 standard deviation (SD) below the young adult reference range (more than –1)
Low bone density (osteopenia):
1 to 2.5 SDs below the young adult reference range (–1 to –2.5)
More than 2.5 SDs below the young adult reference range (–2.5 or less)
If your bone density test result is low:
Low bone density values may be caused by other problems, such as:
Your bone density 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 group.
You may not be able to have the test, or the results may not be helpful, if:
U.S. Preventive Services Task Force, et al. (2018). Screening for osteoporosis to prevent fractures: U.S. Preventive Services Task Force recommendation statement. JAMA, 319(24): 2521–2531. DOI: 10.1001/jama.2018.7498. Accessed October 29, 2018.
National Osteoporosis Foundation (2014). Clinician's guide to prevention and treatment of osteoporosis. National Osteoporosis Foundation. http://nof.org/hcp/clinicians-guide. Accessed October 22, 2014.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Current as of:
September 8, 2021
Author: Healthwise StaffMedical Review: Anne C. Poinier MD - Internal MedicineMartin J. Gabica MD - Family MedicineKathleen Romito MD - Family MedicineCarla J. Herman MD, MPH - Geriatric Medicine
Current as of: September 8, 2021
Author: Healthwise Staff
Medical Review:Anne C. Poinier MD - Internal Medicine & Martin J. Gabica MD - Family Medicine & Kathleen Romito MD - Family Medicine & Carla J. Herman MD, MPH - Geriatric Medicine
To learn more about Healthwise, visit Healthwise.org.
© 1995-2022 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.