How is BMD measured?
BMD is measured by dual-energy X-ray absorptiometry (DEXA). There are 2 types of DEXA scan. One measures BMD in the spine, hip and forearm (3 common sites of fracture in patients with osteoporosis), and the other form of DEXA measures fat and lean tissue (mostly muscle) in the whole body and in various body regions (the trunk, arms and legs). When DEXA is used to measure fat and muscle, the machine can automatically generate a BMD, t-score and z-score for the whole body if the machines computer software is set appropriately, as well as any regions asked of the machine. It was the use of DEXA for the study of lipodystrophy in HIV-infected adults that lead to the observation that some patients had low total body BMD. Although total BMD on soft tissue or bone DEXAs are similar, they are not identical. There may be a substantial difference between a spine BMD value measured on bone DEXA or soft tissue DEXA. BMD should ideally be determined from bone DEXA, as the values are more accurate an
