Bone Density Scan: An Overview
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.
How a Bone Density Scan Is Scored
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 Bone Density Scan Score Mean?
As outlined in the World Health Organization's diagnostic categories, individuals whose bone density scan 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.
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