What is the difference between a DEXA bone density scan and x-ray?

Dose and accuracy. The dexa uses a very small dose of x-ray compared to a regular x-ray and it is designed to measure density not produce a high quality picture. A regular x-ray is designed to produce a high quality picture and is a poor measure of density.
DEXA uses CT. A dexa scan uses cat scan and measures absorption of the x-ray to come up with a bone density measurement that can then be compared to age-matched normals. X-ray is a simple radiograph that makes an image, but is not able to quantitate bone density.
Nothing. The DEXA scan actually uses two low dose X-rays of different energy. By measuring the differences in how they are absorbed, bone density can be calculated.

Related Questions

Can a DEXA bone density scan show something an X-ray doesn't?

Quantify bonemineral. The dexa scan is a special x-ray scan designed to quantify bone mineral density (bmd) in the spine, hips and forearm. These bmd values are calculated by computer, and can help to predict future risks for fractures. Very low bmd can possibly signify 'osteoporosis', while intermediate low bmd can sometimes be considered 'osteopenia'. The bmd is one of many factors used to measure fracture risk. Read more...
Complementary tests. A dexa quantifies the bone mineral density of the bones examined. An x-ray evaluates the bone mineral density qualitatively as well as the integrity of the bone and looks for disorders such as fractures, metabolic abnormalities, cancer. Read more...