DEXA BONE DENSITY SCANS
At Central Primary Care, dual-energy X-ray absorptiometry (DEXA) scans help us to diagnose or assess your risk of osteopenia and osteoporosis, conditions that weaken your bones and makes them more likely to fracture. As well as being quick and painless, a bone density scan is more effective than normal X-rays in identifying even small reductions in bone density. This makes it possible to diagnose changes in your bone density at an early stage, long before you break a bone, and when further loss in bone density can be prevented.
We've put together the following helpful Q&A to review some of the key aspects of DEXA scans.
What is a DEXA bone density scan?
The DEXA bone density scan uses low-dose X-rays to evaluate the density and strength of your bones. During a bone density scan, a DEXA machine is passed over your body. A low level of radiation is absorbed by the bone and soft tissue. Special detectors in the DEXA machine measure how much radiation passes through your bones, and this information is sent to a computer.
Who needs a DEXA bone density scan?
Osteopenia and osteoporosis don't typically cause any symptoms until a bone is broken. Osteopenia and osteoporosis can also affect anyone at any age, although older postmenopausal women are particularly at risk. This is due to declining estrogen levels after menopause, which cause a reduction in bone density.
At Central Primary Care, we may recommend a DEXA scan for you if you have a family history of osteoporosis, you have osteopenia, or you're at an increased risk due to factors, including:.
* You had had a broken bone after a fall or injury, or you have a health condition, such as arthritis, that can lead to low bone density
* You have been taking oral glucocorticoid medications for 3 months or more. Glucocorticoids are used to treat inflammation, but can also cause weakened bones.
* You are a woman who had an early menopause, or you had your ovaries removed before age 45, and have not been prescribed hormone replacement therapy (HRT) that includes estrogen.
* You are a postmenopausal woman and you smoke or drink heavily, have a family history of hip fractures, or a body mass index (BMI) of less than 21.
* You are a woman and have large gaps -- typically more than a year -- between your menstrual periods
In general, the risk of bone health problems is highest in post-menopausal women, and men over 70.
Are DEXA bone density scans safe?
Bone density scans are very safe. They use a much lower level of radiation than standard X-rays, which means that the radiographer (the technical specialist carrying out the scan) can even stay in the scanning room with you during the scan.
To explain further, the amount of radiation used during a bone density scan is very low, equal to less than 2 days of exposure to natural background radiation (NBR). By comparison, a chest X-ray uses the equivalent of about 3 days of exposure to NBR, and a flight to North America is equivalent to approximately a week's exposure to NBR.
Despite their safety, bone density scans are not recommended for pregnant women, due to the risk of even low-level radiation to a developing baby.
What happens during a DEXA bone density scan?
No special preparations are needed, and there are no injections involved in a DEXA scan. You may be able to remain fully clothed, depending on the area of your body being scanned. You will need to remove any clothing with metal fasteners, such as zippers, hooks, or buckles.
The DEXA bone density scan is quick and painless, and usually takes no more than 10 to 20 minutes. You lay on your back on a flat, open table, and keep very still during the scan so the images are not blurred. During the scan, a large scanning arm will be passed slowly over your body. As the scanning arm moves over your body, a narrow beam of low-dose X-rays will be passed through the part of your body being examined. This will usually be your hip and lower spine to check for weak bones.
Bone density varies in different parts of the skeleton, so more than one part of your body may be scanned. The forearm may be scanned for certain health problems, such as hyperparathyroidism, or if scans are not possible in the hip or spine.
Some of the X-rays that are passed through your body will be absorbed by tissue, such as fat and bone. An X-ray detector inside the scanning arm measures the amount of X-rays that have passed through your body.
This information captured by the scan ultimately produces an image of the scanned area, as well as data regarding bone density in key areas.
You'll be able to go home after you have had the scan.
What do the results of a DEXA bone density scan mean?
A bone density scan compares your bone density with the bone density expected for a young healthy adult or a healthy adult of your own age, gender, and ethnicity. The difference is calculated as a standard deviation (SD) score. This measures the difference between your bone density and the expected value.
The difference between your measurement and that of a young healthy adult is known as a T score,
The difference between your measurement and that of someone of the same age is known as a Z score.
The World Health Organization (WHO) classifies T scores as follows:
* above -1 SD is normal
* between -1 and -2.5 SD is defined as mildly reduced bone mineral density (BMD) compared with peak bone mass (PBM)
* at or below -2.5 SD is defined as osteoporosis
If your Z score is below -2, your bone density is lower than it should be for someone of your age.
Although these results provide a good indication of your bone strength, the results of a DEXA scan will not necessarily predict whether you'll get a fracture. For example, some people with low bone density will never break a bone, whereas others with average bone density may have several fractures. These differences are due to factors such as age, sex, fitness history, family history, medical history, certain medicines, and whether you have previously had a fall.
Your Central Primary Care doctor will consider all of your individual risk factors -- before recommending any drug treatments or lifestyle changes for better bone health.