Definition: Bone mineral density (BMD) is a measure of calcium and other minerals in bone. Denser bones tend to be stronger. NIAMS says the most common test is a central DXA (or DEXA) scan, an x-ray test that usually measures the hip and spine, the bones that break most often.
A T-score compares your BMD with a healthy young adult, set at 0. Postmenopausal women and men 50 or older get a T-score. NIAMS gives these bands:
| T-score | What it means |
|---|---|
| -1 or higher | Healthy bone |
| -1 to -2.5 | Osteopenia, low bone density less severe than osteoporosis |
| -2.5 or lower | Possible osteoporosis |
NIAMS says fracture risk rises 1.5 to 2 times with each 1-point drop.
Premenopausal women, men under 50 and children get a Z-score, which compares BMD with healthy people of the same age, ethnicity and sex. NIAMS says a Z-score of -2.0 or less is low and may point to bone loss from medicines or other conditions.
NIAMS notes that the U.S. Preventive Services Task Force recommends a BMD test for women over 65, and for younger women past menopause who are at increased risk of an osteoporosis-related fracture.
DXA results are used to diagnose osteoporosis and to check whether treatment such as a bisphosphonate is working. Scans are usually far apart, so logging the date, the T-score at each site and the machine or clinic makes later results easier to compare.
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