In Part 1 of this series, we learn what to reliably expect from a DEXA scan. In this post, we’ll learn about the limitations of the DEXA scan and why they should NOT be the sole determinant of fracture risk.
In the previous post, the variability of results was reviewed:
What time of year you have the DEXA scan done
Inconsistencies between different DEXA machines and operator skill set
Results are less accurate for those with slim builds and smaller skeletons
Given these variations – less than 5-6% change from previous scans is insignificant or at least not as actionable as bigger changes
In this post we’re going to cover two additional limitations of the DEXA scan:
A DEXA scan is an indirect, not a direct, measure of bone health, and therefore
It tells only part of the story about fracture risk
First, its important to remember that the DEXA scan is designed to measure the mineral content of bone, think of this as the quantity of bone, which is only part of the story in terms of determining bone health. Our bone’s mineral density accounts for about 60% of the bone’s fragility. Bone fragility reflects the ability of your bones to resist fracture.
Determining bone fragility is not only the result of how much bone you have, as measured by the DEXA scan, but the strength, or quality, of that bone. The DEXA scan cannot inform us of the strength or the quality of bone, only the quantity. “So, while DEXA evaluation of BMD is seen as the “gold standard”, it can only account for 60% of the measure of bone fragility.”1
So, the next question is “How do we measure bone quality or strength?”
Well that’s a bit more challenging because many factors go into determining bone strength and the technology required is not readily available as part of the standard medical protocol.
There is however a test that is starting to be included with the DEXA scan that can measure bone quality – the Trabecular Bone Score, or TBS.
Trabecular Bone Score relies on software that is added to some DEXA scan machines and is capable of providing additional information about the quality of bone to complement the information from the DEXA on quantity of bone. At this time, the cost of a TBS is an out-of-pocket expense although efforts are being made to have Medicare include it in their coverage. And there are very few facilities in North America that have DEXA machines outfitted with TBS software.
While its helpful to know one’s bone mineral density via the DEXA scan, it is only an indirect measure of fracture risk. And risk of fracture is the real concern. It’s the hip or spinal fracture that will potentially limit one’s independence, vitality and quality of life.
Increased risk of fracture accompanies increased fragility of bone. And fragility of bone is determined by both bone mineral density (quantity) and bone strength (quality). Many people don’t realize that while osteoporosis (almost) always causes bone fragility, bone fragility is not always caused just by osteoporosis. In fact more fragility fractures occur in women with low to moderate bone loss as measured by DEXA scan compared with women who have a diagnosis of osteoporosis.
Fracture risk is the result of multiple factors, some of which are the result of bone quality and quantity but also one’s daily choices as well as genetics.
To determine your risk of fracture, you may want to review these top 7 bone fracture risk factors:
Use of steroids (cortisone, prednisone) both orally, topically or inhaled
Parental hip fracture
Low body mass (20 or lower) as determined by Body Mass Index (click here)
Rheumatoid arthritis and other auto-immune illnesses
Prior fragility fracture
Current smoker
High alcohol intake (greater than 2 drinks per day)
You can also do the free online Fracture Risk Assessment Tool (FRAX) .
If you checked off any of these risk factors then its time to prioritize your bone health if you’re not already doing that. There are several ways you can modify your daily choices that can help you build strong, resilient bones naturally.
Want to learn more? Join me at the next FOUNDATIONS OF BONE BUILDING WEBINAR (sign up for the Harbor Healthy Lifestyle Blog for updates). We’ll discuss what you can do to reduce your risk of fracture by identifying the root cause of excessive bone loss and build strong healthy bones for your lifetime…naturally!
1 Fonseca, Helder Sports Med 2014 Jan;44(1):37-53.