Bone Mineral Density Tests: What the Numbers Mean

A bone mineral density (BMD) test measures calcium and other minerals in bone. Bones containing more minerals are denser, so they tend to be stronger and less likely to break. Bones can become less dense as we age or if we develop certain medical conditions. When too much bone is lost, osteoporosis can develop. Osteoporosis causes bones to become weak and brittle, which increases the risk of fractures (broken bones). Bone mineral density testing can: Identify and diagnose osteoporosis. Measure the risk of fractures (broken bones). Monitor the effectiveness of osteoporosis treatment. The most common bone mineral density test is a central dual energy x-ray absorptiometry (DXA or DEXA). DXA uses radiation to measure how much calcium and other minerals are in a specific area of your bone. Because the weak bones that tend to break most often are the hip and spine, DXA usually measures bone mineral density in these bones. If your T-score is: –1 or higher, your bone is healthy. –1 to –2.5, you have osteopenia, a less severe form of low bone mineral density than osteoporosis. –2.5 or lower, you might have osteoporosis . The risk of broken bones increases by 1.5 to 2 times with each 1-point drop in the T-score. If you are a woman in postmenopause or a man who is age 50 or older, your bone mineral density test result will be a T-score. A T-score is the difference between your bone mineral density and 0, which is the bone mineral density of a healthy young adult. The lower your T-score, the higher your risk of bone fracture. If your Z-score is –2.0 or less, your bone mineral density is low. This score could mean that you have osteoporosis caused by medications or other diseases and conditions. If you are a premenopausal woman or a man younger than age 50, your bone mineral density test result will be a Z-score. Z-scores are also used for children. The Z-score is the difference between your bone mineral density and the average bone mineral density for healthy people of your age, ethnicity, and sex. The U.S. Preventive Services Task Force recommends that women over age 65 have a bone mineral density test. The Task Force also recommends testing for women younger than age 65 who have gone through menopause and are at increased risk for an osteoporosis-related fracture. More research is needed before the U.S. Preventive Services Task Force can make a recommendation regarding osteoporosis screening in men. The Task Force encourages anyone concerned about their bone health to talk to their doctor. . It is important that you review your BMD test results with your doctor for a full explanation of what they mean for you. Any diagnoses or treatment recommendations would be based on your BMD test results, age, and other fracture risk factors that you may have. In some cases, your doctor may refer you to a specialist. This content was created by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) with contributions from: National Institute on Aging National Institute of Diabetes and Digestive and Kidney Diseases NIH Office of Research on Women’s Health