Bone scans measure the amount of bone in a particular site of the body, usually the lower part of the spine, the hip, the forearm or the heel. Doctors use the scans to help them to assess the likelihood of future bone fractures and whether any treatment is needed.
What does a bone scan show?

Scans of any bones can predict your overall risk of future fractures. The amount of bone measured by a scanner is often called the 'bone density'. Bone density varies in people just like height but the lower the density the higher the risk of fractures in the future. These scans are much more useful for assessing bone density than X-rays, which can be misleading.
What happens during a scan?

You will need to sit or lie still for a few minutes. No needles are involved. Most scanning machines use narrow beams of X-rays but some use ultrasound instead. The X-ray dose is very small, a fraction of that needed for a chest X-ray.
Why are particular sites scanned?

Particular scans sites are more suitable for certain patients. Scans at the hip, for example, are better for predicting hip fractures but some patients are unable to get into position for them. Scans of the forearm are quick and precise but cannot be used in people who have previously had fractures of both wrists or who have some types of arthritis. Spinal scans tend to give misleading results in people aged over 60, or in people who are unusually thin or fat.
How often should scans be done?

One scan is enough for most people to assess the overall future risk of fractures. A second scan may be needed after two or three years if a new decision is needed about treatment. Scans every two or three years may be needed in patients who have to take steroid therapy long term.
Does a low bone density always mean osteoporosis?

No, other conditions can cause low bone density levels and may also cause fractures. These include osteomalacia (vitamin D deficiency), over-activity of some glands; some disorders of the intestine, and brittle bone disease (osteogenesis imperfecta), an inherited condition that mainly causes fractures in childhood. It is important to rule out these problems, as they require different treatment to osteoporosis.