Bone Mineral Density (BMD)

Bone mineral density, or BMD, is a measurement used to estimate how much mineral is present in bone. In clinical practice it is most commonly measured with dual-energy X-ray absorptiometry, or DXA, at sites such as the hip and lumbar spine. Standard DXA reports an areal BMD in grams of mineral per square centimeter rather than a true three-dimensional density .^1,2

BMD is useful because lower values are associated with lower bone strength and greater fracture risk. Results are often compared with reference populations and expressed as T-scores or Z-scores, depending on the clinical context. These scores are ways of interpreting a measured BMD, not separate measurements of bone. A DXA result also depends on the scanned site, positioning, body and bone size, and artifacts such as degenerative changes .^1,2

BMD should not be treated as a complete description of bone quality. Bone strength also depends on geometry, microarchitecture, turnover, accumulated damage, and other material properties that are not fully captured by a standard DXA measurement. This is why two people with similar BMD values can have different fracture risks, and why fracture assessment considers additional clinical factors alongside BMD .²