Dual-energy X-ray absorptiometry (DXA) is currently the gold standard by which bone mineral density (BMD) is measured. It can be used for the diagnosis, prognosis and monitoring of osteoporosis. Currently, a DXA T-score of ≤ -2.5, or BMD less than or equal to 2.5 standard deviations (SDs) below that of the young-adult mean, is used to diagnose osteoporosis in postmenopausal women and men age 50 years and older. A T-score <-1.0 but >-2.5 signifies Osteopenia or low bone mass, whereas a T-score ≥ -1.0 indicates normal bone density. The relative risk of fracture can be calculated as approximately 2 T-score. When a patient has been treated, the change in BMD can be used to show whether there has been a significant improvement or not. Finally, the Z-score, or number of standard deviations of BMD compared to that of an adult of the same age and sex, if less than -2, can give a clue that there are secondary causes to the bone loss. However, the DXA scan must be done as precisely and accurately as possible, and there may be artefacts that interfere with accurate interpretation.