The amount of bone tissue in a segment of bone. The general premise is that the heavier the bones, the stronger they are; Measuring BMD is the best way to evaluate bone strength and predict fracture risk. Results are reported as T-scores and Z-scores.
Deeper dive
The most commonly used BMD test is called a central dual-energy x-ray absorptiometry, or central DXA test. The test is painless, and similar to having an x-ray. The test can measure bone density at the hip and lumbar spine. According to the NIH Osteoporosis and Related Bone Diseases Resource Center, BMD test results are compared to the bone mineral density of a healthy young adult; the results are given as a T-score. A score of 0 your BMD is equal to the norm for a healthy young adult. Differences between a person’s BMD and that of the healthy young adult norm are measured in units called standard deviations (SDs). The more standard deviations below 0, indicated as negative numbers, the lower the BMD and the higher the risk of fracture.
A BMD test can help a clinician determine appropriate prevention or treatment options. If bone mass is not low enough to be classified as osteoporosis, it may be classified as osteopenia. These conditions can be caused by heredity, low body weight, or a medical condition or medication that negatively affects bone. Although not everyone who has low bone mass will develop osteoporosis, low bone mass is an important risk factor for osteoporosis fractures.
The U.S. Preventive Services Task Force recommends that all women 65 and older should have a bone density test. Postmenopausal women who are younger than 65 and at increased risk of osteoporosis – as determined by a formal clinical risk assessment tool – should also have a BMD test.