A bone density scan determines if you have osteoporosis, a disease that results in the weakening and thinning of bones, causing them to become fragile and likely to break. It can also help detect osteopenia, a condition in which your bone density is less than optimal but not so concerning as to be classified as osteoporosis. A bone density test uses X-rays to measure the level of calcium and other materials in a single segment of bone. This test is usually done on the spinal bone, clavicle bone, hip bone or forearm bone. Most tests require you to lie on a padded platform while a device passes over your body, emitting a very low dose of radiation. The test usually lasts between 10 and 30 minutes and is completely painless. In some cases, you can have a simple bone density test done at your local pharmacy or drugstore. Your doctor will talk with you about what kind of tests are best for your personal plan of care.