A bone density test—also referred to as a DXA scan or a bone mineral density (BMD) test—is the current way to diagnose osteoporosis. The test measures the quantity of bone at specific locations in the body, namely the mid-spine bones (lumbar region) and the upper end of the thighbone where it connects to the pelvis (total hip and its subdivisions—the femoral neck and trochanter).
These locations are used for two primary reasons:
- they have a large quantity of trabecular bone—the spongy, lattice-like bone on the inside- that tends to lose density as we age; and
- measurements taken at these locations can be easily replicated so that we can determine if there are changes in the quantity (density) of bone over time.
The quantitative results of the test are measured in grams and then converted to a T-score to compare your results with what we might expect them to be. Your T-score, along with other risk factors, helps your health care provider assess how likely it is that you will break a bone in the future. Armed with this information, your T-score and your 10-year fracture risk, you can have a conversation with your health care provider about both treating and preventing bone loss.
It is very important to keep all of your BMD test results so you can track your bone health as you age.
What can I expect when I get a bone density test?
The machine used to measure bone density consists of a twin-bed-size padded table with a half-moon arm that passes above your body as you lay face up. The scanner uses a very small x-ray beam to get an image of the bone. A technician or technologist will adjust your position on the bed to view the lumbar spine (lower back) and the hip. The technician will then use the computer to analyze the image and determine the bone density. All completed scans are then read by a trained physician to ensure accuracy of the positioning and analysis before the final report is sent to you and your health care provider.
Generally your health care provider will ask for a DXA of the spine, left hip, right hip or both. It is the recommended protocol from the International Society for Clinical Densitometry (ISCD) to scan two different locations to confirm a diagnosis.
If your health care provider suspects that you may have a spine fracture, he or she may also order an image of your spine from the side. This Vertebral Fracture Assessment, or VFA, helps your health care provider confirm if you have a fracture and determine its severity to help make decisions about how to treat the fracture and prevent other fractures.
There are times when the technician or technologist has challenges getting proper images of your bones at two locations. If you have a hip replacement, the technician will scan your opposite hip. If you have had both hips replaced, the technician will likely scan your forearm. On occasions when a patient has a diagnosis of hyperparathyroidism, the technician will scan the forearm because this condition can cause loss of the kind of bone that is found in the forearm. In all cases, the technician will make every effort to scan two locations on your body.
Is a bone density test safe?
DXA scanners use a very low level of radiation—about 1/10 of the radiation in a chest x-ray or what you’d be exposed to on a airplane flight from California to New York. Bone density testing is a very safe test.
Is there any pain involved in DXA testing?
The DXA test takes 10-15 minutes and is painless. And as long as you are not wearing any metal on your clothing, like zippers and underwire bras, you can keep your clothes on! Your job is to relax on the padded DXA table. The technician will help adjust your legs to get the best image of your spine and hips. As with any x-ray, you will need to keep still for accurate results.
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