Bone Density Scan
Similar to an x-ray, a bone density scan is a painless way to measure your bone health and determine your risk for fracture. This test can also measure your response to osteoporosis treatment and assess your risk for fracture. The results from your scan are compared to two standard norms to determine your score.
What Is a Bone Density Scan?
A bone mineral density scan (BMD), a non-invasive and painless test, is the best way to determine your bone health. Dual energy x-ray absorptiometry (DEXA) scan is the best current test to measure BMD. The scan is quick and painless; it is similar to having an x-ray taken, but uses much less radiation.
A bone density scan can identify osteoporosis, determine your risk for fractures, and monitor your response to an osteoporosis treatment. Different bone density tests may measure your hip, spine, wrist, finger, shin bone, or heel.
Your bone density scan is compared to two norms: "young normal" and "age-matched." Young normal, known as your T-score, compares your bone mineral density to optimal or peak density of a 30-year old, healthy adult and determines your fracture risk, which increases as bone mineral density falls below young-normal levels. Age-matched, known as your Z-score, compares your bone mineral density to what is expected in someone your age and body size. Among older adults, however, low bone mineral density is common, so comparison with age-matched norms can be misleading.
The difference between your bone mineral density and that of a healthy, young adult is referred to as a standard deviation (SD).
What Does Your Score Mean?
As outlined in the World Health Organization's diagnostic categories, individuals whose T-score is within one standard deviation of the "norm" are considered to have normal bone density. Scores below the "norm" are indicated in negative numbers. For example, a score from -1 to -2.5 SD below the norm indicates low bone mass, or osteopenia, and a score of more than -2.5 SD below the norm is considered a diagnosis of osteoporosis. For most BMD tests, -1 SD equals a 10 percent to 12 percent decrease in bone density.