What is bone mineral densitometry (BMD)?
A dual-energy X-ray absorptiometry scan (DXA), or bone density scan, is a special type of X-ray that measures bone mineral density (BMD). It provides information about bone strength or fragility and the risk of fractures or broken bones. The higher the density, generally, the lower the risk of fracture.
The spine and one or both hips are routinely scanned. The forearm might also be scanned if either the hip or spine is unavailable (usually due to surgery). As any condition affecting bone density tends to affect the whole skeleton, a snapshot of a few sites is sufficient to establish the overall bone density. The BMD at the hip and spine has been shown to be the best way of predicting the risk of fracture. (Hendrich 2017)
The National Osteoporosis Foundation recommends that you have a bone density test if:
- you are a woman age 65 or older
- you are a man age 70 or older
- you break a bone after age 50
- you are a woman of menopausal ae with risk factors
- you are a postmenopausal woman under age 65 with risk factors
- you are a man age 50-69 with risk factors
A bone density test may also be necessary if you have any of the following
- an X-ray of your spine showing a break or bone loss in your spine
- back pain with a possible break in your spine
- height loss of ½ inch or more within one year
- total height loss of ½ inches from your original height
(National Osteoporosis Foundation, 2018)
How long does a BMD take?
The examination takes approximately 30 minutes.
What happens when a patient comes in for a BMD?
On arrival for your DXA scan, your height and weight will be measured. This allows the computer to generate information about your bone density.
The most important aspect of a DXA scan is to position the hips and spine in the same way each time you are scanned, so that results are accurate and comparable at each visit. To achieve this, when scanning the spine, a cushioned box will be placed under your knees. The cushioned box allows the small of your back or lower spine to lie flat on the table. To scan the hip, this box is removed and a frame made up of a flat sheet of Perspex with a triangle at one end will be placed between your feet. The frame allows the leg being scanned to be positioned accurately. The foot is strapped to the triangle by Velcro, and the knee can also be held in place by a Velcro strap to keep the leg still. Generally, neither of these positioning maneuvers are uncomfortable or painful. (Hendrich 2017)
How to prepare for a BMD?
On the day of examination DO NOT take calcium supplements or iron tablets. Please bring a list of all your current medication with you to the examination. If possible, please wear clothing without zippers or metal buttons (e.g. jogging suit or leggings).
Hendrich, E. (2017, March 29). Bone Mineral Density Scan (Bone Densitometry or DXA Scan). Retrieved from https://www.insideradiology.com.au/bone-mineral-density-scan/
National Osteoporosis Foundation. (2018) Bone Density Test, Osteoporosis Screening & T-score Interpretation. Available at: https://www.nof.org/patients/diagnosis-information/bone-density-examtesting/ [Accessed 16 Apr. 2018]