Bone density tests are usually done on bones that are most likely to break because of osteoporosis, including:
- Lower spine bones (lumbar vertebrae)
- The narrow neck of your thighbone (femur), next to your hip joint
- Bones in your forearm
If you have your bone density test done at a hospital, it'll probably be done on a central device, where you lie on a padded platform while a mechanical arm passes over your body. The amount of radiation you're exposed to is very low, much less than the amount emitted during a chest X-ray. The test usually takes about 10 to 30 minutes.
A small, portable machine can measure bone density in the bones at the far ends of your skeleton, such as those in your finger, wrist or heel. The instruments used for these tests are called peripheral devices, and are often found in pharmacies. Tests of peripheral bone density are less expensive than are tests done on central devices.
Because bone density can vary from one location in your body to another, a measurement taken at your heel usually isn't as accurate a predictor of fracture risk as a measurement taken at your spine or hip. Consequently, if your test on a peripheral device is positive, your doctor might recommend a follow-up scan at your spine or hip to confirm your diagnosis.