Bone density—also known as bone mineral density or bone mass—is a measurement of the amount of calcium and other minerals present in the bones. It is a main indicator of bone health and structural integrity and is used to estimate the likelihood of future fractures or the development of the progressive disease called osteoporosis. Medical professionals use a number of procedures to accurately measure bone density.
Reasons for Testing
You may receive a bone mineral density test for a number of reasons, including detection of low bone density before you break a bone, prediction of future chances of breaking a bone, confirmation of an osteoporosis diagnosis or monitoring of your body’s responses to bone density treatments.
DXA Bone Density Testing
According to the National Osteoporosis Foundation, the standard way to test your bone density is to measure your spine and hip bones in a procedure called a dual energy X-ray absorptiometry (DXA). In this test, you will lie down on a table in a special facility while your body is scanned with an X-ray imager that passes overhead. The procedure can be performed while you are fully clothed and typically takes 10 to 15 minutes. During testing, you will be exposed to an amount of radiation roughly equal to one-tenth of that used in most chest X-rays. Your hips and spine are usually checked because they are the bones most at risk for dangerous density changes, but a scan of the radius bone in your forearm may be used as a substitute if necessary.
Understanding Testing Results
Once a DXA test is performed, your results will be measured according to standards established by the World Health Organization. This involves comparing your bone density to that found in an average, healthy 30-year-old adult. The differences between the two densities are measured in a unit called a standard deviation (SD). If you are within 1 SD of the young adult average, your bone density is considered normal. If you are between 1 and 2.5 SDs, you are diagnosed with low bone mass. If your measurement is more than 2.5 SDs from average, you are diagnosed with osteoporosis.
In some circumstances, your bone density may also be measured against others in your specific age group. While this comparison can help reveal certain additional conditions or diseases, it is not used to distinguish osteoporosis.
Additional Testing Procedures
You may also be tested through other methods, including a procedure called a quantitative computed tomography (CT) scan. This technique uses a scanner combined with 3-D imaging software to produce detailed pictures of your bones that can be examined and interpreted by qualified specialists. During the roughly 10-minute test, you will lie down on a table that moves you in and out of the CT machine.
Peripheral bone mineral density testing is a less accurate technique that may be used to determine your need for full testing. This procedure, which measures bone density in your wrists, fingers or heels, is typically performed in a doctor’s office or at public health fairs. Consult your doctor for further details of bone density testing.