Dual energy X-ray absorptiometry (DXA) is the current gold standard for the diagnosis of osteoporosis. BMD of the lumbar spine and the proximal femur are the best sites to measure for prediction of future fracture risk. Both sites should be measured (Table 3). DXA is reliable, with a reported precision of about 1%, although in routine clinical practice this is closer to 2%. At this precision level, the least significant change at the lumbar spine would be 5.6% between measurements, with 95% confidence that the change is real.
Each standard deviation (SD) reduction in FN BMD increases the age-adjusted risk of hip fracture by a factor of approximately 2.5 (range 2.0–3.5), while the risk attributable to any minimal trauma fracture is almost the same (range 1.7–2.4). Similarly, each SD reduction in lumbar spine BMD increases the risk of spinal fracture by a factor of approximately 2.3 (range 1.9–2.8). FN and total hip BMD appear to be the best overall predictors of fracture risk. The total hip is the better site for monitoring BMD as it has good precision (less affected by positioning) and is relatively unaffected by osteoarthritis, which can spuriously elevate spinal BMD values, as can vertebral fractures and arterial calcification.1,2