Osteoporosis can be prevented and successfully treated, but like many other diseases, the sooner you start treatment, the better. In the absence of fragility fractures, the diagnosis of osteoporosis is almost completely based on a measurement of bone mineral density (BMD), also called bone density scan. This measurement can be done with a number of measuring devices, but dual energy x-ray absorption (DXA) by the spine and hip is the most common. Since 1994, osteoporosis is classified by comparing a patient’s BMD to that of a young-adult reference population. Results are expressed as a “T-score” and a T-score equal or less than -2,5 (minus 2,5) is strongly suggestive of osteoporosis. A T-score between -1.0 (minus 1.0) and -2.5 is classified as osteopenia (low bone mass) while a result higher than -1.0 is normal.