Some Bone Densitometry Questions and Answers:

What are bone density scans?

Bone scans are measurements of the amount of bone in a particular site, usually the lower part of the spine, the hip, the forearm or the heel. Most scanning machines use narrow beams of x-rays but some use ultrasound instead. These scans are not the same as bone scans carried out with radio-active isotopes in nuclear medicine departments.

What does having a scan entail?

It just means sitting or lying still for a few minutes. No needles are involved! The x-ray dose is very small, a fraction of that needed for a chest x-ray.

What does a bone scan tell us?

The amount of bone measured by a scanner is often called the ‘bone density’. Bone density varies in people – just like height and weight – but the lower the density the higher the risk of fractures in the future. Doctors use the scans, together with other information, to assess the likelihood of fractures and therefore whether any treatment is needed.

Why choose a particular site for scanning?

Scans at any site are approximately as good as each other for predicting overall future risk of fractures. Scans at the hip are slightly better than others for predicting hip fractures. Scans at any site are much more useful than x-rays (which can be quite misleading) for assessing bone density.

There are reasons for choosing particular scan sites for particular patients. 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. Scans of the spine tend to give misleading results in people aged over 60, or in people who are unusually thin or unusually fat. Some people are unable to get into the position needed for scans of the hip.

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 whether to stop or start 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. There are other conditions that cause low figures for bone density and may cause fractures. These include osteomalacia (vitamin D deficiency), overactivity of some glands, some disorders of the intestine, and brittle bone disease (osteogenesis imperfecta), an inherited condition mainly causing fractures in childhood. It is important to eliminate these problems because their treatment is different from that of osteoporosis.