About the Test
Purpose of bone density testing
The purpose of a bone density test is to determine whether you may be at an increased risk of bone fractures. The most common uses of bone density testing are to screen for, diagnose, and monitor health conditions involving weakened bones known as osteopenia and osteoporosis. Osteopenia is a reduced amount of bone mass. Worsening osteopenia can become osteoporosis, a disease defined by brittle bones that are more likely to break.
Screening refers to checking for disease when no signs or symptoms are present. Osteoporosis is more common in people who have certain risk factors. These people may benefit from tests that can detect osteoporosis early and before it has caused symptoms.
Diagnosis is testing to determine the cause of disease after a patient already has symptoms. Sometimes the first sign of bone loss is a broken bone, even from a minor fall. Bone density testing after a bone fracture can show whether a person has osteopenia or osteoporosis that makes them more prone to future broken bones.
Monitoring is observing how a person’s condition changes over time. In people who have osteopenia and osteoporosis, a bone density test can track their bone health and see whether treatment is working.
What does the bone density test measure?
The bone density test measures the density or strength of your bones, which is also known as bone mineral density (BMD).
The most common bone density test uses a technology called dual-energy x-ray absorptiometry (DXA or DEXA), so the test is frequently known as a DXA or DEXA scan. These scans send a thin beam of low-dose x-rays through the bones being examined. DXA machines have special computer software that uses the images to calculate bone density.
The bones that are scanned in a bone density test can vary based on the purpose of testing. In most cases, the density is measured in only a few places, but scanning of the whole body may be performed in certain circumstances.
When should I get a bone density test?
Bone density testing may be appropriate in a number of situations to detect osteopenia or osteoporosis.
As a screening test, bone density testing is recommended by the U.S. Preventive Services Task Force (USPSTF) for all females who are 65 and older because of their elevated risk of osteoporosis. The USPSTF also recommends screening in postmenopausal females younger than 65 years who are at an increased risk of bone loss or bone fractures.
Some factors that increase the risk of weakened bones include:
- Body weight under 127 pounds or body mass index (BMI) under 21
- Family history of osteoporosis
- Use of certain medications that can weaken bones
- Medical conditions such as diabetes and rheumatoid arthritis
- Breaking a bone after age 50
- Early menopause
- Long-term use of alcohol or tobacco
- Lack of physical activity
- Insufficient intake of certain vitamins and minerals such as calcium and vitamin D
Routine screening for osteoporosis in older males is not recommended by most medical experts. However, bone density screening may be beneficial in males who have risk factors that make them more likely to have weak bones or osteoporosis.
Bone density testing may be appropriate as a diagnostic test in people who have suffered a fracture, especially after a relatively minor injury. In these cases, testing can help determine if weakened bones contributed to the fracture and if a person is more vulnerable to additional broken bones in the future.
In people who have already been diagnosed with osteopenia or osteoporosis, repeat bone density tests may be used to monitor the status of their bones and check to see whether treatments are having an effect on their bone health.
It is important to talk to your doctor who can help determine if bone density testing is right for you.
Finding a Bone Density Test
How to get tested
Many bone density scans require a prescription or a referral from your doctor. The testing can then be performed in a hospital or radiology clinic that has the equipment to do a bone density scan.
In some cases, a bone density scan can be done on the smaller bones in the wrist, fingers, or heel. This type of peripheral DXA scan may be offered at a local pharmacy, clinic, or health fair without a prescription.
Talk to your doctor or pharmacist for more information about the different types of bone density tests that are available and where they may be offered.
Can I take the bone density test at home?
A bone density test cannot be taken at home. Instead, testing is available at various hospitals, health centers, clinics, and private medical offices.
How much does the bone density test cost?
The cost of a bone density test can vary based on where and how the test is performed and whether you have health insurance coverage.
Medicare and most health insurance companies will cover the costs of a bone density test if your doctor prescribes it and you meet criteria for testing. Contact your insurance provider to ask whether the plan will pay for testing and if there are any required copays or deductibles.
If you do not have health insurance, talk to your doctor, radiologist, or a hospital administrator about the cost of testing and whether any programs are available to reduce costs for people who are not insured.
Taking a Bone Density Test
The bone density test is done on an outpatient basis in a hospital, radiology office, or health center. The test is usually completed within 10 to 30 minutes.
There are two types of DXA scans. Both types measure bone density but in different areas of the body.
The most commonly used type of bone density test is called a central DXA scan. Central DXA machines are larger and located in many hospitals and clinics. This type of scanner is typically used to assess bone health by measuring bone density in the hip and lumbar spine, two areas that are at risk of fracture with low bone density.
A peripheral DXA scan uses a smaller machine and measures bone density in your wrist, fingers, or heel. These machines may be found in medical offices, pharmacies, mobile health vans, or at some health fairs.
Before the test
A bone density test requires little to no preparation. You can eat normally and take your usual medications, but you may be advised to avoid calcium supplements for at least 24 hours beforehand. You may be asked to fill out a medical questionnaire about your health history including current medications prior to taking the test.
Before the bone density test you may receive guidance from your doctor, including:
- On test day, avoid wearing any garments or accessories with metal that might interfere with the x-ray images such as zippers, belts, buttons, jewelry, keys, eyeglasses, dental appliances, wallets, and purses.
- Wear loose, comfortable clothing.
During the test
For a central DXA scan, you will lie on your back on a padded table. You may be asked to lie flat with your legs straight out in front of you or with your knees bent and your lower legs on a small padded box.
A scanning machine with an overhead arm will pass over your lower spine and hips. At the same time, another scanning machine will pass beneath you. The images from the two scanners will be combined and sent to a computer.
You must remain very still during the test. You may be asked to hold your breath for a few seconds to reduce the possibility of blurred images.
A peripheral DXA scan is much simpler. You place your finger, hand, forearm, or heel in a small portable device. You keep your hand in the device for only a few minutes while the scan is performed.
After the test
Bone density testing is a fairly quick, painless, and simple procedure. Side effects are uncommon, and there are no restrictions on your diet or activities after your bone density test.
Bone Density Test Results
Receiving test results
For most DXA scans, a radiologist with special training in reading and interpreting images of the body will view your bone density scans. The radiologist will send a signed report to your doctor who can explain the results to you. You will usually get the results within a few business days.
For some peripheral DXA scans, the initial results may be available within a few minutes from the person who conducts the test.
Interpreting bone density test results
Bone density test results are reported as T-scores and Z-scores:
- T-scores compare your bone density to that of a healthy young person with normal bone mass. The T-score is considered the more important of the two scores as it better represents bone mineral density and bone health.
- Z-scores compare your bone density to that of other people your age. Doctors typically look more closely at the Z-score for premenopausal females, males under 50, and children.
For both T-scores and Z-scores, a higher number is associated with greater bone density.
Normal bone density refers to a T-score between +1 and -1. If you have normal bone density, you may not need treatment or to make any changes to your diet or activity level.
Low bone density refers to a T-score between -1.1 and -2.4. The term doctors use to describe this level of lower bone density is osteopenia. If you have osteopenia you may be at risk of developing osteoporosis. To prevent future bone loss, your doctor may make certain medication and lifestyle recommendations.
Osteoporosis refers to a T-score of -2.5 or lower. A diagnosis of osteoporosis means you have a significantly higher risk of bone fractures. As a result, your doctor may recommend medications combined with calcium and vitamin D supplements.
These categories of results on a bone density test are summarized in the following table:
| Bone density levels | T Score Range |
|---|---|
| Normal bone density | -1 and above |
| Low bone density Osteopenia | Between -1 and -2.4 |
| Osteoporosis | -2.5 and lower |
Your doctor may consider the results of your bone density test along with other factors to help determine your overall risk of fractures. In some cases, they use a special formula to calculate a risk score. This information can help determine whether any treatment is needed to support your bone health.
It is important to always discuss your test results with your doctor who can explain their significance in your specific situation.
Are test results accurate?
Central DXA scans offer a high degree of accuracy and estimation of bone density. Medical experts consider DXA scans to be the most accurate way of testing for osteoporosis and monitoring treatment efficacy.
Peripheral DXA scans do not have the same level of precision as central DXA scans but can still provide meaningful information about the risk of fractures in certain bones.
While DXA scans are accurate in most situations, they are not as accurate in people who have a spinal deformity, fractures or arthritis in their vertebrae, or a history of spinal surgery.
Do I need follow-up tests?
Follow-up testing can depend on the type of bone density test you had and the test results.
If you had a peripheral DXA scan and the results indicated that you may be at risk of bone fractures, you may be advised to have follow-up testing with a central DXA scan.
If you have completed an initial central DXA scan, ask your doctor about any recommended follow-up tests or procedures. The schedule for follow-up varies based on your risk factors and initial test result.
People with a higher risk of fractures may have a repeat central DXA scan every two years. People with more moderate risk may have repeat testing every 3 to 5 years, and people with less risk may be tested every 10 to 15 years.
Repeat scans may be most beneficial for people who are taking medication to treat osteoporosis. Repeat testing helps to determine the efficacy of treatment. Repeat testing is also recommended for people who have medical conditions that can cause bone loss in order to determine whether they need to begin treatment.
If your doctor recommends future bone density testing, it’s important to try to have the scan done at the same facility as the initial test. There are different models of DXA machines, and for accuracy, bone density measurements obtained on different machines should not be directly compared.
Questions for your doctor about test results
After you receive your bone density test results, it may be helpful to make a list of questions for your doctor. Examples of questions include:
- Is my bone density in the normal range?
- Do I need follow-up testing? If so, which test would you recommend?
- Do you recommend any dietary changes or medications at this time?
Vertebral fracture assessment
An additional procedure called vertebral fracture assessment (VFA) may be included as part of a central DXA scan. VFA is a low-dose x-ray examination of the spine. It does not measure bone density but is instead a way to check for vertebral fractures. The presence of vertebral factors can indicate a higher risk of fractures elsewhere in the body.
DXA scans vs. computerized tomography (CT) scans
A computed tomography (CT) scan uses x-rays to create pictures of cross-sections of the body. In general, a DXA scan is considered a more accurate way of assessing bone density than CT scans.
However, CT scans may be used in situations where DXA scans have limitations. Spinal fractures, spinal deformities, and spinal surgery can interfere with the accuracy of DXA scans. In patients with these health issues, a CT scan may provide more accurate information about bone health.
DXA scans vs. ultrasound
Ultrasound is a procedure that uses high-frequency sound waves to make images of the body’s internal structures. A DXA scan is preferred over ultrasound for measuring bone density. There are limited guidelines for interpreting ultrasound tests to predict fracture risk or diagnose osteoporosis. For these reasons, ultrasound is normally only used as a bone density test when DXA scans are not available.
