Bone Mineral Densitometry
Bone mineral densitometry (BMD) uses a very low-dose X-ray machine that evaluates bone loss commonly associated with osteopenia or osteoporosis. Sometimes, physicians or patients will refer to a BMD scan as a bone mineral density test or DEXA scan. The test uses two low-energy X-ray beams to examine the strength of your bones, identify potential fracture risk, and evaluate the efficacy of therapy.
Bone density tests are most commonly performed on the lumbar spine, hip, and forearm, as these bones have been shown to generate the most reliable measurements for predicting fractures and monitoring treatment. Osteoporosis Canada recommends BMD testing and X-rays of the spine as part of their world-class Fracture Liaison Service model.
Additionally, these three imaging locations are the basis of the World Health Organization’s algorithm for predicting risk fracture in the assessment of osteoporosis. The radiation dose with bone densitometry is minimal and is similar to the exposure you get when you go through an airport security scanner.
Who Should Consider a Bone Density Test?
- Both men and women over age 65
- Post-menopausal women 50 or older with additional risk factors
- Men 50 or older with additional risk factors
Additional risk factors include:
- Early menopause (before age 45)
- Fracture from standing height or less after age 40
- Any spinal or hip fracture
- High alcohol or smoking intake
- Low body weight (less than 132 pounds)
- Disease or conditions such as rheumatoid arthritis, Cushing’s disease, malabsorption syndrome, hyperparathyroidism, or chronic inflammatory conditions
Detecting Osteoporosis with BMD
Bone mineral density scans are used to detect calcium levels, bone loss, and structure fragility, and to assess future fracture risk. This information is incredibly useful for physicians when determining if a patient has osteoporosis or osteopenia, or is at risk for compromised bone structure in the future. It’s important to educate yourself about bone loss symptoms, exercises, and treatment to help prevent the degradation of your body.
What Happens During my Bone Density Exam?
- At the time of booking, you will be asked to wear clothing that does not contain any metal (snaps, buttons, zippers) for your appointment. If you forget the day of your exam, you may be asked to change into a gown when you arrive; we do not want any metal on your clothing.
- You will be weighed and your height measured before your scan.
- Our scanning beds have a maximum weight restriction of 300 pounds. If you are over 300 pounds, we can instead scan your wrist.
- You will be positioned on a bed by our technologist. We will use a foam block to elevate your legs in an upright position to align the spine for optimal measurements.
- The scan should take approximately 10 minutes. Please remain as still as possible for your scan, as movement may blur the images.
- Using dual-energy X-ray absorptiometry, we will calculate your bone mineral content.
- If there is any chance that you are pregnant, please talk to your doctor before coming in for your bone density scan.
- A scanner will pass over you and examine your lower spine or hip or, if we’re completing the modified version of the exam, we will scan your wrist.
- After the scan is complete, one of our radiologists will review the results and send a detailed report to your doctor. We try our best to send the results as soon as possible, usually within one business day.
- All DEXA scans (BMD and body composition analysis) use ionizing radiation. Therefore, there must be zero chance a patient is pregnant. We ask all females between 11 and 55 years about their last menstrual period to determine the possibility of pregnancy.
- We ask this personal question to protect a fetus from radiation exposure; please do not be offended. If there is any chance you are pregnant, please tell your doctor before coming to your DEXA scan.
- Recent changes by the Alberta Government to the Schedule of Medical Benefits (SOMB) Health Service Code X128 state that patients seeking a bone mineral densitometry scan are only allowed to have one scan every two years.
- Patients considered “high risk” for osteoporosis may have a bone density scan more frequently when referred by a specialist. Specialist examples include endocrinology, metabolism, gastroenterology, surgery, internal medicine, nephrology, orthopedic, pediatric, or rheumatology.
Understanding Your Bone Density Results
Bone mineral densitometry tests will provide you with a T-score and a Z-score.
For adults 50 years and older, the bone mineral density classification will be determined using the lowest T-score for the lumbar spine, hip, neck, radius, and total body. If the T-score is greater than or equal to -1.0, you have normal bone mass. If the T-score is between -1.0 and -2.5, you have low bone mass (osteopenia). If the T-score is less than or equal to -2.5, you likely have osteoporosis.
For adults 18 to 49 years, the classification will be determined using the lowest Z-score. Our radiologist will compare this Z-score to a statistical average for the appropriate age group. A Z-score alone is not used to diagnose osteoporosis or osteopenia, but it does provide valuable insights for patients and physicians.
Patients with Z-scores above -2.0 are considered to have normal bone density. If your Z-score is -2.0 or lower, your bone density is below the statistical average. Your physician will use these results and other clinical risk factors to determine your 10-year fracture risk (FRAX).
Our technologist will position you on a bed with a foam block underneath your legs. This position helps align your spine for optimal measurements. If you exceed the 300-pound weight limit of the machine, we will position you beside the scanner with your arm extended.
If you have an Alberta Health Care card or valid healthcare card from out of province, there is no cost for a bone density test (except Quebec).
Bone density tests typically take 20 minutes to complete. The most significant factor impacting duration for a scan is patient mobility.
Bone Density Test vs. Bone Scan
There are many different names for a bone mineral densitometry scan. Often patients or physicians refer to it as a bone density test, bone mineral density, bone mineral densitometry, BMD, DEXA scan, or even DXA. All these names refer to the same exam. Sometimes DEXA or DXA is used for a body composition scan, as both exams typically use the same X-ray technology.
However, these exams are not to be confused with a bone scan. While the term bone scan is very close to all the previous names listed above, it is in fact a very different type of diagnostic imaging exam.
Bone scans are a nuclear medicine exam that involves injecting a radiopharmaceutical into the body, which is later scanned to form diagnostic images. These radioisotopes travel through your body and accumulate at imperfections in the bones. A specialized diagnostic scanning machine pinpoints isotope accumulations, which are indicative of microfractures.
In a bone density test, radiation emission originates from the scanner, outside of your body.
Conversely, radiopharmaceutical injections used in a bone scan emit radiation from inside the body, after the injection.
The purpose of a bone density test is to measure how porous or dense the bones in your body are. It is not meant to find microfractures like a bone scan.
Patients often confuse the two exams when checking in with our receptionists or booking with our patient care coordinators. While the requisition provided by your physician should tell us precisely what test to perform, sometimes mistakes are made when completing a referral.
When a patient is adamant that they are supposed to get a specific imaging exam, our reception team may phone the referring physician’s office to confirm everything before proceeding. Calling the referring physician is an important step, as it ensures we are performing the right diagnostic imaging test.
While the exam preparation for both tests is the same, we must not confuse the two scans, as both exams have very different goals. We also don’t want to waste anyone’s time – yours, the technologist’s, or your referring physician’s. Most importantly, we want to adhere to ALARA principles and ensure we are not exposing you to unnecessary radiation.
Moving Forward After Your Results
If your physician diagnoses you with osteoporosis or osteopenia, you do have options. If you have low bone mass, it is commonly recommended that you increase your weight-bearing exercise and focus on your nutrition. Specifically, ensure you are getting enough vitamin D and calcium. For a complete guide, visit the National Osteoporosis Foundation's website for more information on calcium and vitamin D recommendations for osteoporosis.
Furthermore, if the results show you have osteoporosis, your physician may prescribe a medication to reduce bone breakdown. It is also crucial that you make lifestyle changes, similar to what those impacted by osteopenia must do.
Planning your next appointment? Learn more about bone density test preparation and find the clinic most convenient for you.