By now, every woman has heard that she should take measures to help prevent osteoporosis. In addition to making sound diet and lifestyle choices, having a Bone Mineral Density Test is a great tool when developing a preventative care regime for this degenerative disease. We investigate Bone Mineral Density Testing to help you make an informed decision the next time you see your health care provider.
Definition
Bone mineral density (BMD) tests, also known as bone densitometry or bone mass measurement tests, measure the density of minerals present in a particular segment of bone through the use of x-rays. This measurement is then compared to the ideal bone mass of a healthy, young adult.
While there are several types of machines used to test bone density, BMD tests fall into two categories: central and peripheral. Central machines are considered to be more accurate and measure density in the hip, spine, or total body. Central BMD devices are large and the tests are typically conducted in a hospital or medical facility. Peripheral machines are smaller, portable devices that measure the bone density of the finger, wrist, kneecap, shin bone, or heel and are oftentimes conducted at local health fairs and drugstores.
BMD tests should not be confused with bone scans. Bone scans typically require an injection of radioactive material in order to detect bone abnormalities such as inflammation and cancer.
Testing for Fracture Risk
According to the National Osteoporosis Foundation (NOF), roughly 10 million Americans suffer from osteoporosis and another 34 million are estimated to have low bone density (or osteopenia), putting them at an increased risk of breaking a bone.
Not only is BMD testing the only way to diagnose osteoporosis but it has been shown to be an accurate method for predicting the risk of future fractures. Physicians can analyze BMD test results to assess the possibility of future fractures much in the same way that blood pressure indicates the risk of stroke. In general, the lower the bone mineral density, the higher the risk of fracture.
Doctors prefer to measure bone density in the hip and spine is because Individuals with osteoporosis have a greater chance of fracturing these bones. For this reason, central BMD test results are a more effective predictor of fracture risk in other bones.
BMD testing is recommended for all women, age 65 and older, men, age 70 and older, and any individual with one or more risk factors. If you are at risk for osteoporosis, you should discuss BMD testing with your doctor.
What You Can Expect
There are several different types of machines used to obtain a bone density measurement. The most commonly used central densitometry machines are the DXA (Dual Energy X-ray Absorptiometry or DEXA) and the QCT (Quantitative Computed Tomography). DXA is the preferred and most accurate method of testing for bone density. Both the DXA and QCT devices are large machines that use x-ray technology to determine bone density, although the amount of radiation used is approximately one tenth of that used for a chest x-ray.
The procedure is quick and painless. While lying on a padded platform, the arm-like imager passes over without touching your body. The entire process takes only about 5 to 10 minutes to complete.
Some of the different types of peripheral bone density tests include pDXA (Peripheral Dual Energy X-ray Absorptiometry), QUS (Quantitative Ultrasound) which uses sound waves to measure density at the heel, shinbone, and kneecap, and RA (Radiographic Absorptiometry) which uses an X-ray of the hand and a small metal wedge to calculate bone density.
Peripheral densitometry machines are smaller, portable versions of the central densitometry devices that either use x-ray technology or, less frequently, ultrasound to determine bone mass. Since these units measure bone density on the periphery of the body (e.g. finger, wrist, or heel) the results are not indicative of osteoporosis. Rather, peripheral densitometry tests are used as a screening method to determine if further BMD testing is warranted.
What the Results Mean
Bone density test results are indicated with two numbers, a T-score and Z-score. Both scores are calculated as a standard deviation and indicate how your bone density compares to a “norm” or ideal density. The closer the score is to 0, the more closely it reflects the standard. A negative score indicates that the bone is less dense than the standard and a positive score indicates the bone is more dense than the standard.
The T-score compares your bone density to that of a healthy, 30 year old adult of the same sex. The Z-score compares your bone density to what is expected for someone of the same age, sex, weight, and ethnic origin.
T-scores above -1 indicate normal bone density. A score between -1 and -2.5 indicates signs of osteopenia. A score below -2.5 indicates osteoporosis.
Z-scores above -2.0 are normal according to the International Society for Clinical Densitometry (ISCD).
There are conflicting viewpoints with regard to frequency of retesting. The American Medical Association advises against repeat testing as a method of monitoring osteoporosis treatment because changes in bone density can oftentimes be mistaken for simple mechanical error and vice versa. However, for an individual taking osteoporosis medication, the National Osteoporosis Foundation does recommend retesting every two years.
One drawback to BMD testing is that while the test can confirm whether or not you have or are at risk for osteoporosis it does not point toward a cause for the bone loss. Additionally, due to excessive weight or thickness of body tissue, test results can be affected and results may be inaccurate. Central BMD tests can also be costly. Without insurance DXA scans can cost approximately $200, however most insurance policies will cover the cost if an individual has one or more risk factors.
The bottom line is that there is only one way to find out if you have osteoporosis – by having a central bone mineral density test. Considering that the process is quick and painless, this test is just as important as knowing your blood pressure and cholesterol levels. At the bare minimum, take the time to find a screening and find out if you are at risk.