Conventional x-rays are not used to diagnose osteoporosis; however, osteoporosis can sometimes be seen on x-rays. The x-rays used to diagnose a fracture can show osteoporosis, but only if you have a significant amount of bone loss—that is, 30% to 40%. There are, however, other tests that can be used specifically to evaluate your bone health. All bone mineral density (BMD) tests are safe, painless, and noninvasive. Most of the tests subject you to no more radiation than that received from the atmosphere during a cross-country airplane trip. One of the BMD tests uses ultrasound technology.
You should not be tested for bone density if you are pregnant or have had other x-ray studies that require dye within 2 weeks of bone density testing. Testing is limited for individuals who weigh more than 250 pounds. This is both because many machines can only hold individuals who weigh 250 pounds or less and because the more soft tissue there is, the harder it is to distinguish it from bone, making it difficult to obtain accurate results. The “gold standard” (best test) for diagnosing osteoporosis or identifying osteopenia is dual-energy x-ray absorptiometry (DXA).
Because your hip, spine, or whole body may be evaluated using DXA, you will need to lie down on an x-ray type of table while a machine takes measurements of your bone density. The measurements and images of your bones are sent to a computer nearby, usually in the same room. Figure 7 shows a woman undergoing bone mineral density testing with a DXA machine. DXA scan measurements are very precise and use very little radiation.
They are also the best tests for monitoring changes in bone density and evaluating effectiveness of treatments over time. It is best to have your bone density measured on the same machine and by the same technician each time you have it done, if possible. The presence of fractures, osteoarthritis, and calcifications (calcium deposits) can interfere with the accuracy of BMD testing, particularly of the spine (see Questions 31–32).
The peripheral dual-energy x-ray absorptiometry (pDXA) scan uses the same technology as the DXA but measures bone density in your wrist, forearm, finger, or heel. If a central DXA test shows osteoporosis at one or more sites, your clinician will most likely do some laboratory tests prior to confirming the diagnosis because your clinical history and laboratory results are needed before deciding if it is osteoporosis alone, or if there is another problem causing secondary osteoporosis or medication(s) causing bone loss.