If you’ve been asked to have a bone density test, here’s everything you need to know.
Bone density tests are commonly used to determine if someone has osteoporosis – a disease that weakens bones, causing them to become thinner and more brittle. This means they’re more likely to break or fracture.
It’s helpful to detect osteoporosis early on to establish whether your bone density has decreased, before you suffer any fractures. It also helps in assessing your risk of developing fractures in future. A bone density test may also be used to confirm a diagnosis of osteoporosis, and to monitor the success of treatment you receive.
What is a bone density test?
A bone density test is used to measure the density of your bones, using X-rays to measure the calcium and other bone minerals within a section of bone. It is different to a bone scan, which is used to detect fractures, cancer, infections and other bone abnormalities. Unlike a bone scan, which usually requires an injection, a bone density test is easy, quick and pain-free.
Some simple bone density tests can even be done at your local pharmacy, but other times it will need to be done at a hospital. If your test takes place in a hospital, you should let your doctor know if you may be pregnant. You should also tell your doctor if you’ve recently received a barium exam or been injected with contrast material for a CT scan or nuclear medicine test. This is because the contrast materials might interfere with your test.
What happens during the test
A bone density test is usually conducted on the areas must susceptible to fractures from osteoporosis – namely the spine, hip and forearm. Your test will likely examine your lower spine bones (called the lumbar vertebrae), the neck of the thighbone, which is nearest your hip joint), and the bones in your forearm.
There are two types of equipment used to conduct bone density tests – a central device and a peripheral device. If you have your test in hospital, it’s normally done with a central device. You’ll lie on a padded table while a mechanical, overhead ‘arm’ performs an X-ray on the area of bone being measured. The test usually takes between 10 and 30 minutes, and exposes you to less radiation than that emitted during a chest X-ray.
If you’re tested with a peripheral device instead, this can sometimes be done in a pharmacy. A peripheral device is a small machine that measures the bone density in your peripheral bones – such as your heel, wrist or finger. However, because bone density levels are different throughout the body, measurements taken at your spine or hip provide greater accuracy. This means that if you test positive for thinning bones during a peripheral device test, you may need a second scan with a central device to confirm your diagnosis.
Understanding your results
The results of your bone density test are reported in two numbers: your T-score and your Z-score.
The T-score is based on your gender and compares your bone density levels with those of a healthy young adult of the same gender. It gives you the number of units (also known as standard deviations) by which your bone density is above or below the average.
If your T-score is -1 or above, you have normal bone density. If it’s between -1 and -2.5, your bone density is below normal, and you may develop osteoporosis in the future. If your score is -2.5 or more, this indicates you likely have osteoporosis.
Your Z-score compares your results to the norm for your age, sex, weight, and ethnic or racial origin. If you have a Z-score of -2 or lower, there may be a cause of abnormal bone loss other than aging. However, if your doctor can identify the cause, you may be able to treat the underlying problem and slow or stop bone density loss altogether.