Bone mineral density (BMD) is the measurement of the most important minerals that are present in a person's bone structure. Most popularly, these minerals include calcium, which is largely responsible for maintaining the strength and integrity of bones. Bone mineral density is measured by using a computed tomography (CT) scan or X-ray, and this measurement becomes increasingly important as a person ages.
Mineral content in bones naturally decreases as a person gets older, and the loss of too much calcium can result in osteoporosis and in brittle bones that break easily. An accurate bone mineral density measurement can foreshadow later problems. With enough warning, one can begin preventative measures, such as the taking of calcium supplements, getting proper exercise or even starting hormone therapy can begin.
Bone mineral density is something that should most concern women who are more than 65 years old. Men can also get osteoporosis, but it is more frequently found in women. Screenings are recommended for postmenopausal women.
People who are concerned about bone mineral density can speak with their doctor or other medical professional to request an ultrasound. This non-invasive test, usually performed on a person's heel, and it will not accurately measure an exact percentage of bone mineral density, but it can be used to look for problems. From there, other tests can be performed to receive more precise results. BMD tests are typically done every two years, and they are often done as a follow-up to treatment for osteoporosis because the number will reveal how well the treatment is working.
There are numerous ways BMD can be accurately measured. Quantitative computed tomography is a CT scan used to measure the bone density of the spine. Dual-energy X-ray absorptiometry uses a pair of X-rays to measure bone density in a person's hip and spine. This noninvasive method can detect bone loss as small as 2 percentage points.
Peripheral dual-energy X-ray absorptiometry is similar to dual-energy X-ray absorptiometry. The peripheral version of this test can measure the density of different bones, such as those of the arms and legs. Dual photon absorptiometry also measures bone density in the spine and hip, this time using small amounts of a radioactive substance.
The spine and hip are typically tested, because these are among the most likely bones to break in older individuals. The results are usually in the form of a T-score, which compares the results of the tests to the BMD of a normal, healthy, 30-year-old individual. The BMD of most people this age falls within a narrow range, making it an excellent control group. A negative number means that the tested bones are thinner than a typical 30-year-old, and a positive score means that they are thicker. When results are given in the form of a Z-score, this means that an individual's test results are being compared to those of other people of a similar race, age and gender.