This test measures a person's bone density in order to diagnose osteoporosis, a disease in which the bones become less dense, which in turn can result in fractures, deformity, and disability. Testing bone mineral density helps to both diagnose the disease and tell how far it has progressed. Women are at higher risk for osteoporosis than men, particularly after the menopause.
This test is likely to be ordered by a healthcare professional for: a postmenopausal woman, especially if she has had a fractureany woman older than 65 regardless of risk factorsa woman considering treatment for osteoporosis, if BMD testing would affect the decisiona woman who has been on hormone replacement therapy for a long time
Most methods for measuring bone mineral density are fast and painless. The methods involve taking either dual energy x-rays (DEXA, the most commonly used modality) or CT scans of the bones of the spine, wrist, arm, or leg. One new method that was recently approved by the FDA uses ultrasound of the heel. It only takes about a minute to do and is less costly than the other methods, but is also a less sensitive test.
Most centers ask the woman to undress and put on an exam gown. She will also be asked to remove any jewelry or metal that could interfere with the test. During the DEXA test, the woman lies face up on the x-ray table while the system scans an area of her body, usually the lower spine or hip. The test takes only a few minutes and the x-ray dose is small.
During a CT scan, the person lies on a narrow table that slides into a doughnut-shaped gantry. This is a frame that houses the various parts of the CT machine. A series of x-rays are then taken of the area being tested, usually the lower spine and then the hip, by a camera that revolves completely around the area. The picture this method makes is a highly detailed cross-section of the area. The CT scan is more likely to be used if there is a suspected compression fracture of the vertebrae related to osteoporosis.
A woman will be asked if she is pregnant. If she is, the test is deferred until after the baby is born, in order to avoid the radiation exposure to the unborn child. In addition, the woman should also ask her healthcare professional for any special instructions needed to prepare for the test.
By comparing the numbers calculated from the test with an established standard of bone density, a healthcare professional can diagnose osteoporosis. The person's chances of having a bone fracture can also be estimated. This information can be used to determine if the individual is a candidate for medications that can decrease osteoporosis.