A bone density test determines if you have osteoporosis — a disorder characterized by bones that are more fragile and more likely to break. In the past, osteoporosis would be suspected only after you broke a bone. By that time, however, your bones could be quite weak. A bone density test enhances the accuracy of calculating your risk of breaking bones.
A bone density test uses X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone. The bones that are most commonly tested are in the spine, hip and sometimes the forearm.