Dual-energy X-ray Absorptiometry or DXA measures Bone Mineral Density or BMD. Tests on DXA machines are commonly called bone density scans. These machines became available over 20 years ago. The on board computer gives a simple number for a reading. It looked like a very simple and accurate way to test for Osteoporosis. We now know that it is neither.
DXA measures the Bone Mineral Density of the hips and spine, and sometimes the forearm. BMD is the most easily measured aspect of bone health. However, it is not the whole story. Vertebral Fracture Assessment or VFA is the other half of the story. DXA alone misses 15 to 20% of Osteoporosis patients.
Reading a DXA is different from reading a regular X-ray. DXA is similar to, but different from, other X-ray technologies. Even DXA machines are different. DXA by Hologic and DXA by GE use different technologies even though both are just called DXA.
To be accurate, a DXA report must be checked and often corrected by someone who has taken a special course. The International Society for Clinical Densitometry (ISCD) has developed standards to follow in reading DXA. These standards have changed over time to reflect new knowledge.
Jay Ginther, MD
2008/Revised November 2010