Early Detection for Osteoporosis
About This Imaging Test
A DEXA (Dual Energy X-ray Absorptiometry) scan — also called DXA or a bone densitometry scan — uses X-ray imaging to measure bone density, also called bone mass. The test can identify osteoporosis, which is the gradual loss of calcium in the bones that increases the risk of fractures and breaks. By diagnosing osteoporosis at an early stage, your doctor may be able to help you slow progression of the disease, preventing further bone loss and bone fractures.
A DEXA bone density scan is not the same as a bone scan which is a nuclear medicine image used to detect arthritis, fractures, infections and tumors in the bones.
How the Test is Performed
Bone density testing can be done 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.)
How to Prepare for the Test
If you are or could be pregnant, tell your provider before this test is done.
How the Test will Feel
The scan is painless. You 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 of osteoporosis. You are more likely to get osteoporosis if you are:
- A woman, age 65 or older
- A man, age 70 or older
You may be asked not to eat or drink anything for 4 to 6 hours before the scan.
Tell your health care provider if you are afraid of close spaces (have claustrophobia). You may be given a medicine to help you feel sleepy and less anxious, or your doctor may suggest an open MRI, in which the machine is not as close to the body.
Women under age 65 and men ages 50 to 70 are at increased risk of osteoporosis if they:
- Have a broken bone caused by normal activities, such as a fall from standing height or lower (fragility fracture)
- Have chronic rheumatoid arthritis, chronic kidney disease, or eating disorders
- Have early menopause (either from natural causes or surgery)
- History of hormone treatment for prostate cancer or breast cancer
- Have had a significant loss of height due to compression fractures of the back
- Have a strong family history of osteoporosis
- Take corticosteroid medicines (prednisone or methylprednisolone) every day for more than 3 months
- Take thyroid hormone replacement
- Have three or more drinks of alcohol a day on most days
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:
- T-score compares your bone density with that of a healthy young women.
- Z-score compares your bone density with that of other people of your age, gender, and race.
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.
What Abnormal Results Mean
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:
- Between -1 and -2.5, you may have early bone loss (osteopenia).
- Below -2.5, you likely have osteoporosis.
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.