A risk factor assessment is an important first step in alerting you to
your risk for osteoporosis. However, it is not a scientific way to predict whether your bones will become
porous. Many people who develop osteoporosis have few of the risk factors — a fact we are trying to understand through research into the causes of
osteoporosis.
This is why medical testing is so important. The tests are known as Bone
Mineral Density (BMD) tests and the technology that they use is known as bone densitometry. These tests are
safe, painless and accurately measure the density of your bones. A BMD test can tell you whether or not you
have osteoporosis and how likely you are to develop it in the future, and can help you to make decisions that
may prevent fractures or further bone loss.
About BMD testing
Who should have a BMD test?
Bone densitometers (the machines that perform the test) are available on
a limited basis across Canada, and thus, individuals who are suspected to be at high risk are generally given
priority for this testing. Like any other diagnostic test, you must be referred to a diagnostic facility by a
physician. OC recommends that individuals who, in consultation with their physicians, discover that they are
at high risk of developing osteoporosis have this test in order to plan a proper healthcare
strategy.
Specifically, there are several situations where a bone density test is
recommended:
- You are 65 or older.
- You and your physician have done a risk factor assessment and have
determined that you are a high-risk individual.
- You have lost four or more cm in height overall or two or more cm in one
year. You have kyphosis (excessive backward curvature of the spine resulting in either a hump or a more
gradually rounded back).
- You are taking glucocorticoid medication, and want to determine if you
are losing bone mass and whether treatment for osteoporosis is required.
- You have recently had a fracture in which osteoporosis is suspected and
you want to make decisions about further diagnosis and treatment options.
- You already have osteoporosis and you and your physician are monitoring
the effectiveness of the treatment.
If you and your doctor agree that your bones need to be monitored, make
sure you are re-tested on the same BMD machine whenever possible.
What exactly happens during a bone densitometry
test?
The most common bone density test in use today is called dual energy
x-ray absorptiometry (DXA). This test involves lying on a table for several minutes while a small x-ray
detector scans your spine, one hip, or both. You may be asked to lift your legs onto a support to straighten
your back for the test. The test is safe and painless and does not require any injections or any other
discomfort. You receive a very small amount of radiation from a DXA test, approximately the same amount you
are exposed to if you fly from Toronto to Vancouver.
How does a bone densitometer measure bone
density?
Think of the light shining through the curtains of your home on a sunny
day. The amount of light that reaches your eye depends on the thickness of the curtains. If your curtains are
very thick, very little sunlight passes through them. If, however, you replace them with a thinner fabric,
the light coming through to you will increase substantially. Similarly, a bone densitometer uses a detector
to measure the transmission of small amounts of x-rays (light) through your bones. The amount of light that
passes through the bone is measured, thus providing a radiologist with a picture that indicates how dense
(thick or thin) your bones are.
