A bone density (DEXA) scan allows your doctor to assess your bone health. In this post, our radiologists in Ottawa explain the test, why you may need it, how the procedure works and more.
What is a bone density scan?
By measuring your bone density - how strong your bones are - we can tell whether you have osteoporosis. The most commonly used test is the dual-energy X-Ray absorptiometry (DXA or DEXA), which assesses bone health and your risk of fracture as a result of osteoporosis. Risk of fracture is influenced by factors including body weight, age, history of previous fractures, family history of osteoporotic fractures and lifestyle such as excessive alcohol consumption and smoking.
This safe, non-invasive and painless scan typically focuses on the spine and hip. If these can’t be tested, the radiologist can scan your forearm. The test involves minimal exposure to ionizing radiation to produce pictures of the inside of your body to measure bone loss.
Why would I need a bone density scan?
The DEXA scan is the most commonly used and the most standard method for diagnosing osteoporosis. Women are most often affected by this condition post-menopause, but it is also sometimes found in men and rarely in children. Osteoporosis is defined by gradual structural changes to your bones, thinning bones and bone loss. The condition increases your risk of bone fragility and fracture.
We can also use these scans to monitor the impact of treatment for osteoporosis and other conditions that result in bone loss.
We strongly recommend bone density testing if you:
- Are not taking estrogen and are a woman who is post-menopausal
- Are a tall post-menopausal woman (over 5 feet 7 inches) or thin (less than 125 pounds)
- Have X-Ray evidence of vertebral fracture or other symptoms of osteoporosis
- Have had a fractured bone after only mild trauma
- Have type 1 (formerly known as insulin-dependent or juvenile) diabetes, kidney disease, liver disease or a family history of osteoporosis
- Use medications known to cause bone loss
- Have a thyroid condition such as hyperthyroidism
- Have a parathyroid condition such as hyperparathyroidism
- Have a personal or maternal history of smoking or hip fracture
- Are a man with clinical conditions related to bone loss, such as chronic liver or kidney disease or rheumatoid arthritis
How should I prepare for a bone density scan?
A bone density scan requires little to no special preparation. Eat as you normally would on the day of your exam. If there is a possibility you may be pregnant, or if you’ve recently received an injection of contrast material for a radioisotope scan or CT scan, let your doctor know as they may have you wait a few days before scheduling this test.
Please arrive at our clinic 15 minutes before your scheduled appointment time so you’ll have time complete the examination questionnaire. Bring a list of any medications you’re currently taking.
Remove all jewellery and other accessories in the area to be scanned and wear loose, comfortable clothing. Wear pants with no metal, buttons or zippers, but they should have a waistband. Avoid wearing shirts that have designs or buttons. If you can, wear a sports bra - and avoid wearing a bra with hooks or underwires. You may be asked to wear a gown.
For at least 12 hours before your exam, do not take calcium supplements.
What will happen during my bone density scan?
This quick scan typically takes about 20 minutes, depending on the number of areas that need to be tested.
You’ll be asked to lie on the exam table, then our technologist will place you in the correct position so the appropriate scans can be done. The scanner will move over specific areas of your body, using low-dose X-Rays located below your body to send data to a computer. The detector (imaging device) will be positioned above your body.
The data will then be converted and displayed on a monitor. Stay very still as the test is being done - you may be asked to hold your breath.
What are the limitations of a bone density scan?
Some common limitations of a bone density test include:
- While a DEXA scan cannot predict who will experience a fracture, it assesses your relative risk and is used to determine whether you will need treatment.
- For those who have a spinal deformity or have had previous spinal surgery, DEXA use is limited since vertebral compression fractures or osteoarthritis can interfere with the accuracy of the test. CT scans may be more useful.
- Follow-up DEXA tests should be performed at the same place and ideally with the same machine. Bone density measurements taken with different equipment cannot be compared directly.
What happens after the exam?
The radiologist will interpret the images and send a report to your doctor, who will review the results with you. There will be two scores indicated on your test results:
This number is used to predict your risk of developing a fracture, and to determine whether treatment is needed. It compares the amount of bone you have to a young adult of the same gender with peak bone mass. A score of -1 and above is thought to be normal. A score of -1.1 and -2.4 is categorized as low bone mass (osteopenia). A score of -2.5 and below is classified as osteoporosis.
This score measures the amount of bone you have compared to other people in your age range, and of the same gender and size. If this score is unusually high or low, it may indicate that more medical tests are needed.
Between scans, small changes may occur due to differences in positioning and are not typically significant.
Your doctor may decide you need to be evaluated on a regular basis every three years, to check if your bone density has significantly increased or decreased. Your doctor will also consider your risk for bone fracture when deciding whether therapy or testing are needed.