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117: DEXA vs REMS: What's the Difference?
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In this episode of the Movement Logic Podcast, Sarah discusses two primary methods for measuring bone density: DEXA (Dual-Energy X-ray Absorptiometry) and REMS (Radiofrequency Echographic Multi-Spectrometry). The episode explains what each method measures, their technologies, reliability, and practical applications. It compares their availability, cost, accuracy, and limitations. DEXA is recognized as the clinical gold standard but has some limitations, while REMS, although newer, shows promise with advantages in certain clinical situations.
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References:
77: Are You Getting DEXA Scammed?
Best Practices for Dual-Energy X-ray Absorptiometry Measurement and Reporting
New technology REMS for bone evaluation
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Transcript
Introduction and Mission
00:00:00
Speaker
I'm Laurel Biebersdorf, strength and conditioning coach. And I'm Dr. Sarah Court, physical therapist. With over 30 years of combined experience in fitness, movement, and physical therapy, we believe in strong opinions loosely held. Which means we're not here to hype outdated movement concepts.
00:00:15
Speaker
or to gatekeep or fearmonger strength training for women. For too long, women have been sidelined in strength training. Oh, you mean handed pink dumbbells and told to sculpt? Whatever that means, we're here to change that with tools, evidence, and ideas that center women's needs and voices. Let's dive in.
Understanding Bone Density Measurements
00:00:44
Speaker
Welcome back to the Movement Logic Podcast. I'm Dr. Sarah Court, I'm physical therapist, and today we're talking about two different ways that you can measure bone density, DEXA and REMS. So if you've been told by your doctor that you need a bone scan, odds are they meant a DEXA scan. But if you tend to get into the research or hang out in those kinds of corners of the internet, you've probably seen people talking about REMS as better than DEXA or the future of bone health, right? So in this episode, we're going to lay out what is DEXA exactly, what it measures, what's the tech, how reliable is it, And then we're going to do the same for REMS, what's actually happening and what the research says.
00:01:27
Speaker
And then we're going to compare them directly in terms of availability, cost, accuracy, limitations, and when you might reasonably choose one over the other.
00:01:38
Speaker
This is not supposed to be Team DEXA versus Team REMS, right? This is what does the evidence say and how do you make a decision as a human living in a real world with a budget and an actual human body, right?
Movement Logic Tutorials Sale
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But before we get into that, I wanted to let you all know, listeners, that we are running a site-wide sale on all of our tutorials. Yes, we're called Movement Logic Tutorials because when we started, we made tutorials. We started making the tutorials when Movement Logic was founded in 2017, and there's six different ones organized by body area. low back, pelvic floor, hips, shoulders, feet and ankles, and neck. Every Movement Logic tutorial contains hours of anatomy, kinesiology, myth-busting, and most importantly, dozens of exercises that will help you train strength, flexibility, and functional movement for whatever you or your clients want to do in life. And the more you invest, the more you save.
00:02:39
Speaker
If you purchase one, you get 10% off. If you purchase two, you get 15% off. And we only offer this sale once a year. So if this sounds interesting to you, you're going to want to click on the link in the show notes and go to the sale page and snap up a few of those tutorials.
00:02:56
Speaker
Okay, let's get into it. Let's start with the one that's been around the
How DEXA Works and Its Limitations
00:03:00
Speaker
longest. That is the DEXA scan. DEXA stands for, oh, this is so hard to say, dual energy X-ray absorbtiometry.
00:03:08
Speaker
I always want to add an extra R or an N in there. So the way that the technology works is it uses two low-dose X-ray beams at different energy levels. That's why it's dual energy X-ray.
00:03:23
Speaker
And they go through your body. Usually we are looking at the lumbar spine and the hip and the femoral head area. And the scan measures how much those beams are weakened as they pass through the bone and the soft tissue.
00:03:40
Speaker
Because bone and soft tissue absorb x-rays differently at different energies. And then it uses that information to calculate the bone mineral density area. in grams per square centimeter.
00:03:53
Speaker
So by comparing these two different beams, the software can basically subtract out soft tissue and then estimate how much mineral is in that slice of bone. Now, something important to know about a DEXA scan is that it's 2D, just like an X-ray, it's not 3D. So it measures density per area. So it's really, it's measuring a slice of your bone. It's not measuring the volume density.
00:04:17
Speaker
And it gives you a snapshot of how much mineral is in a region, but it doesn't give you any information about the micro architecture of the bone itself, right? How is that bone put together? More details about thinness or thickness and the architecture of the shape. No, it just gives you a picture how much mineral is in this slice.
00:04:36
Speaker
And then it gives you a score and the scores are typically either what's called a T score or a Z score, right? If you've had a DEXA scan, you've seen these. So a T score, is how many standard deviations your bone mineral density is above or below the mean of a young adult reference population of the same sex.
00:05:01
Speaker
So what that means is, let's say we're trying to diagnose osteoporosis in a woman who's 60 years old, they're gonna compare it to a 25 year old woman and see what the difference is in that bone mineral density, right? So this is how we diagnose. And then the Z-score is a slightly different comparison. It's how many standard deviations you are from the age-matched mean.
00:05:26
Speaker
So it's looking at compared to people your age and asking, is this low for you given your age, right? So T-score is more a sense of how much bone mineral density have you lost over your lifespan. And the Z-score is better if it's someone who shouldn't really have osteoporosis. And we're comparing you to someone your age and this looks really weird compared to someone your age, right?
00:05:53
Speaker
And then the scoring works
Reliability and Limitations of DEXA
00:05:57
Speaker
like this. A T-score of one or greater is considered normal. A T-score between one and minus 2.5 is osteopenia,
00:06:07
Speaker
which is considered a precursor to osteoporosis. And we did a whole episode called Are You Getting Dexa Scammed, which I'm going to link in the show notes that talks about the origin of how they came up with these different cutoffs.
00:06:22
Speaker
It's not as scientific as you think. And then the final one is if you have a T-score of two point minus 2.5 or lower, that is considered osteoporosis.
00:06:36
Speaker
We can use the DEXA results with risk assessment tools like the FRAX tool. And there are some DEXA scans that also look at your trabecular bone score, which is a sort of analysis of the texture of the image and gives a little more information about that micro architecture.
00:06:57
Speaker
And you can also look at vertebral fracture assessment, which are these images of the spine to look for compression fractures. Not all scanners will do those two additional pieces of information.
00:07:11
Speaker
But a modern DEXA scan can tell you, like, here's your bone density at certain sites. Here's how that compares to normal population. And then if you get these additional scores, it's like, here's your fracture risk. And here's whether your spine looks like it's already been fractured or degraded in a way that just looking at the bone mineral density might not tell us.
00:07:32
Speaker
With all that said, typically people are just getting the T score. They're not often getting this additional vertebral fracture assessment or trabecular bone score. So how reliable is a DEXA scan? Well, it's still considered the clinical gold standard for diagnosing osteoporosis, for estimating fracture risk, and monitoring how people are responding to any intervention or treatment that they're getting.
00:07:56
Speaker
Many, many international guidelines, best practice statements still are built around the DEXA. And in terms of how precise and accurate it is, because one of the things that DEXA is sort of renowned for is actually not being particularly accurate machine to machine.
00:08:14
Speaker
But if you're getting repeated readings on the same machine, it's going to be accurate in terms of you and then you a year from now. But if the machine is well-maintained and the technician knows what they're doing, it's very precise.
00:08:32
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When it's working well, errors are on the around like a couple of percent, which is why they will space out your DEXA scans at least one year apart.
00:08:44
Speaker
That way they make sure that they see meaningful changes and it's not just an error on the machine. Now, Your bone mineral density as scored on a DEXA is strongly associated with your fracture risk.
00:08:58
Speaker
The lower bone mineral density you have, the higher risk you have a fracture. But that is not the complete picture at all because a large part of your fracture risk is how much of a falls risk you are.
00:09:12
Speaker
you're not going to just walk down the street and break a hip, most likely, right? You would have to be unbelievably osteoporotic for that to happen. But if you fall and there is a you know a forceful landing and you have osteoporosis, yes, you have a chance of breaking a bone. So having the bone mineral density that is osteoporotic is putting you at a higher risk, but only if you're someone who's also falls risk.
00:09:38
Speaker
Okay, so let's talk about ways that the DEXA is not necessarily the most perfect. This is not an exhaustive list, but this is a few things that can happen. So the DEXA can actually overestimate bone density when there is osteoarthritis and people have big osteophytes, like big bony bone spurs, when there's a vertebral compression fracture, sometimes when there's scoliosis or other changes to the spine.
00:10:08
Speaker
If there is any metal hardware in the spine, these can all artificially jack up your spine bone mineral density and make this bone look stronger on paper than it actually is.
00:10:20
Speaker
One of the other limitations is this, what I mentioned before, it's a 2D measurement. It's the area, it's not the volume. And it doesn't separate out cortical bone, which is the type of bone that's in the shaft, from trabecular bone or spongy bone, which is at the end of the bone itself. Two people could have this exact same area BMD, but very different bone quality and fracture risk for that reason. It doesn't take into account body size and body composition. So for people who have very large bodies or very small bodies or have a lot of adipose tissue, that can influence the readings. Now, machine software tries to correct for that, but it's not perfect. And your T-score depends on something called a reference database. What populations are considered normal, how race or ethnicity is handled, and there are ongoing debates about whether some of those reference sets either over-diagnose or under-diagnose in certain populations.
00:11:18
Speaker
And lastly, you get a tiny dose of radiation. It's it's less radiation than taking an an airplane ride across the country, but it's not nothing. This really only matters if you are getting a lot of scans, you are very young, or you are pregnant.
00:11:32
Speaker
So our DEXA option, it's widely available. It's well-validated. It's considered the clinical gold standard. It's in international guidelines, but it also is not a perfect test. It has some blind spots. So let's keep that in mind as we turn our attention to the new kid on the block and the new up and coming scanner on the block is called REMS.
Introduction to REMS Technology
00:11:58
Speaker
REMS stands for Radiofrequency Echographic Multispectrometry. Nope. Radiofrequent Echographic Multispectrometry.
00:12:09
Speaker
Couldn't they make it easier to say? All right, so if your DEXA is based on x-rays, you can think about the REMS as being based on ultrasound. So REMS uses a specialized ultrasound transducer that is placed over your lumbar spine or the proximal femur, and And it collects the raw radio frequency ultrasound signals that bounce back off of the bone.
00:12:34
Speaker
And then instead of just looking at a grayscale image, like if you've ever had a regular ultrasound and you've glanced over at what the technician is looking at, it's just this very fuzzy, I never understand how they can see anything, but this sort of like fuzzy image, right? But instead of that, the software analyzes the signals across a spectrum of frequencies, right? That's why it gets to call itself multispectrometry.
00:12:58
Speaker
And that it compares those patterns to a large reference library of signals from people with known bone status, meaning osteoporotic or not osteoporotic, to estimate the bone mineral density and then also give a fragility measure related to the quality of the bone.
00:13:16
Speaker
So REMS is non-ionizing. There's no x-rays, there's no radiation, so that's good. Echolite is a company that you might have heard of if you are in the REMS world, and it has a REMS system that is portable.
Comparing DEXA and REMS
00:13:29
Speaker
It can be used in smaller clinics, and it has FDA clearance in the U.S. for assessing bone density at the spine and at the hip. I'm not sure if it's cleared for use ah in other countries yet.
00:13:41
Speaker
So what a REMS exam gives you, like what it outputs, is a BMD value at your lumbar spine and the femoral neck and hip. And it's calibrated to be comparable to DEXA so that you're getting similar numbers, right?
00:13:55
Speaker
It also gives you a T-score and a Z-score using the same points for osteoporosis, osteopenia, and a normal BMD. And then it gives you something called a fragility score, which which is meant to reflect bone quality and short-term fracture risk beyond bone mineral density alone.
00:14:13
Speaker
So on paper, it looks a lot like a DEXA scan. Plus, it's just got this extra metric that's trying to capture bone quality. So let's talk about the research around REMS. Since it is the new scanner on the block, we got to see what the research says about it. So there are multiple studies and reviews that show a strong correlation between REMS bone mineral density value and a DEXA bone mineral density value.
00:14:43
Speaker
So that means they, in these research papers, gave someone a DEXA scan and then gave them a REMS scan and compared the al outcome. And so, for example, a 2024 review reported a very high correlation coefficient between the REMS and the DEXA at the lumbar spine and the femoral neck.
00:15:03
Speaker
And another validation study found very small mean differences between REMS and DEXA BMD, which suggests that it's a very good correlation. So at a sort of gross level, REMS and DEXA are broadly measuring the same thing.
00:15:21
Speaker
So if we're going to ask them the next question, which is, if DEXA is the gold standard, how well does REMS identify osteoporosis? And a 2021 study by Amirim
00:15:34
Speaker
of adult women found that REMS had high sensitivity and specificity, which is what you want in a tool that is measuring something. You want it to be very sensitive to what it's trying to measure, and you want it to really specifically measure that thing and not other things for diagnosing osteoporosis compared to DEXA. And the study concluded that it is a promising alternative in settings where DEXA isn't available.
00:15:58
Speaker
And a broader review in 2023 summarized that REMS showed good diagnostic concordance with DEXA. In other words, most of the time it puts people in the same category of normal osteopenia or osteoporosis.
00:16:13
Speaker
However, in some studies, REMS T-scores tended to be slightly lower than DEXA T-scores at the spine and at the hip, which may mean that REMS could classify more people as having osteoporosis. So that might be a good thing, right? It might be catching the people that the DEXA is missing, or it might be over-diagnosing osteoporosis.
00:16:38
Speaker
That, as far as I know, is still being worked out, whether this is a good thing or a bad thing. So the the thing that people are excited about with REMS the most is the fracture prediction and bone quality.
00:16:55
Speaker
So some longitudinal studies suggest that REMS indices, especially the fragility score, may have superior performance in predicting short-term fracture risk compared to BMD alone.
00:17:09
Speaker
There is also newer emerging work that is suggesting that REMS may better identify osteoporosis in people who already have bone fragility fractures compared to ADEXA, which means it might be a more accurate tool to use in a case where you've got a lot of confounders, like you have a bunch of fractures in your spine already or where it's more complicated, right?
00:17:37
Speaker
So a big selling point with REMS is that If you recall, some of the limitations that we found with DEXA is that it could overestimate spine bone mineral density when there are conditions like osteoarthritis, scoliosis, vertebral fractures.
00:17:55
Speaker
A lot of studies are suggesting that REMS readings are less affected by these things and may classify more of those patients as having osteoporosis. which matches their actual fracture history better.
00:18:10
Speaker
So a DEXA scan might pick up on someone's osteoarthritis or their scoliosis or a prior fracture and bump up what their bone mineral density is because of those inaccurate readings.
00:18:27
Speaker
But the REMS scan is not as affected by these things and therefore may give a more accurate reading for someone who actually does have osteoporosis that is missed on the DEXA scan.
00:18:40
Speaker
So REMS is not magic, it's not error proof, but You know, it looks very promising. It has a solid correlation to DEXA. It has potential advantages in certain clinical situations. And from a marketing perspective, it's radiation free and it's portable.
00:19:00
Speaker
And while the body of evidence around it is growing, it's still a smaller body of evidence and much newer than the decades of DEXA data that we have.
00:19:12
Speaker
So let's put them head to head and see how they actually compare in certain categories that we care about.
Availability and Accuracy of DEXA and REMS
00:19:17
Speaker
So in terms of availability and guideline status, a DEXA scan is widely available in hospitals, imaging centers, mobile units. It's the reference standard in osteoporosis guidelines. It's used in clinical trials, drug-approved studies. It's plugged directly into tools like the FRAX tool. Whereas the REMS, the Echolite device is a lot newer. The FDA clearance has only been since 2018. It has a growing footprint in Europe and in some cities in the US, particularly specialty clinics or cash pay clinics, but it's not
00:19:55
Speaker
as ubiquitous as DEXA is yet. Most major guidelines are still going to reference the DEXA. REMS might be mentioned or it might not be. So if you ask your average primary care clinician for a bone density test, you're getting a DEXA. You're not getting REMS.
00:20:10
Speaker
And then let's look at their accuracy. What are they actually good at? So in terms of measuring BMD, they have a strong correlation at the spine and the hip. They are not giving us wildly different numbers for the majority of people.
00:20:23
Speaker
And there are some studies that find the REMS-T scores are a little bit lower, where more people are classified at osteoporotic than the DEXA scan.
00:20:34
Speaker
When a spine is tricky, let's say when there's things going on that might cloud the information, DEXA can get fooled by osteoarthritis, scoliosis, fractures, hardware, which would then cause it to overestimate someone's bone mineral density when in fact the spine is more fragile. REMS seems to be less vulnerable to these issues, and it may classify more of those patients as osteoporotic, which would be a more accurate reading.
00:21:03
Speaker
In terms of fracture prediction, the bone mineral density reading that we get from ADEXA is really well validated for predicting fracture risk. especially when you use something like the FRAX tool and combine it with clinical factors like, are you a falls risk? Do you have a smoking history? Things like that.
00:21:18
Speaker
The REMS measures, especially its fragility score, also show, in some case, superior fracture prediction in initial studies, but we don't have a lot of long-term, large-scale data for it yet. So they're at least comparable. The REMS might be a little bit better, but we don't fully know.
00:21:37
Speaker
In terms of bone quality, DEXA by itself is mostly about the quantity of the mineral. You don't get a lot of information about the trabecular bone architecture.
00:21:51
Speaker
When you go in to get a DEXA, you're not generally getting these additional scores as well. Whereas REMS has a bone quality index in the standard report. And their you know marketing claims are that they measure bone quality, not just bone density.
00:22:07
Speaker
And it's encouraging to read the research on that, but it is, again, still evolving. We don't have a large, long-term body of evidence for how useful this bone quality index is and what information it's actually giving us that is superior to a DEXA.
00:22:26
Speaker
If we're talking about radiation, this one's pretty straightforward. With a DEXA, you get a pretty low dose hit of radiation, Less than a cross-country flight, but it's still radiation. REMS uses ultrasound, so there's no radiation. So if you're someone who's getting scanned a lot, if you're young, if you're pregnant, the no radiation part starts to become more relevant.
00:22:46
Speaker
So let's talk about the cost and who pays, because this is the the part of the story that might actually be the most influential for you if you are going to be making a choice, if there is even a
Cost and Insurance Considerations
00:22:58
Speaker
choice for you to make. REMS is not available everywhere yet, right? So if you're going to get a DEXA scan, typical prices in the US are somewhere between, if you're paying without insurance, somewhere between $150 $300 typically.
00:23:11
Speaker
Most insurance companies, including Medicare, cover a DEXA when you have certain risk criteria. Like if you are at risk for osteoporosis, this can completely reduce or eliminate any out-of-pocket cost.
00:23:25
Speaker
So if it's prescribed by your doctor, most likely it's going to be covered by your insurance. If you're just like, hey, I want to get a DEXA scan, you're going to be paying out of pocket. If we look at REMS, REMS typically at this point is seen in cash pay clinics.
00:23:39
Speaker
And these clinics typically advertise individual scans in the $200 to $350 range. Sometimes you also get a consult. Insurance coverage is patchy.
00:23:50
Speaker
Some places will bill it as an office visit. Others will be out of pocket. Getting your insurance to cover it is going to be iffy at this point because depending on how the place you visit bills it, if they bill it as an office visit, you might be able to get away with insurance. If they don't,
00:24:08
Speaker
Because DEXA exists and it's already covered by most insurance, your insurance company is probably not going to cover a REMS if there's not some really specific reason that you need it. Because DEXA and REMS correlate so well, it's unlikely that insurance is going to see a reason for you to get a REMS instead of a DEXA. So if you wanted to get a REMS nowadays, you're probably paying out of pocket.
00:24:29
Speaker
So if we want to look at this from a practical point of view, when does each one make the most sense?
Choosing Between DEXA and REMS
00:24:38
Speaker
DEXA is the choice if you need an official osteoporosis diagnosis so that this is all covered by your insurance and you have a treatment plan that is based on clinical guidelines. You also want to get a DEXA if your clinician wants to use the FRAX tools,
00:24:53
Speaker
If you are in a health system where DEXA is covered and easy to get and REMS just doesn't even exist yet, bottom line, if you're following mainstream guidelines and need something that every clinician and insurer recognizes, DEXA is still queen.
00:25:10
Speaker
REMS might have an edge, right? REMS starts to look too attractive. if you can't get x-rays or you don't want to expose yourself to radiation, but again, it's very low, it's very attractive if your spine is, for want of a better word, a hot mess on an x-ray, if you've got osteoarthritis, if you've got prior fractures, if you've got hardware, if you have scoliosis. So those are reasons why REMS might be the better choice.
00:25:38
Speaker
In some places, because REMS is portable, you might have a mobile or a local REMS service where it's available where a DEXA may not be. And the other time that REMS is a better choice is if you're really interested in bone quality metrics like a fragility score.
00:25:56
Speaker
With the caveat, with the understanding that the evidence is promising, but it is new. So you always want to be a little cautious, not jump two feet in just for that reason.
00:26:09
Speaker
If you have these kind of specific needs, REMS might be the right choice for you, not just a shiny new toy. Now, the marketing claim is that REMS is more accurate than DEXA.
Assessing REMS Marketing Claims
00:26:22
Speaker
But what the literature actually says is that it's broadly comparable to DEXA. It may be more accurate in certain artifact-heavy situations. The fragility measures that it puts out might be very good at predicting short-term fracture risk, but we don't have enough data to look at long-term fracture risk.
00:26:42
Speaker
And most major guidelines still treat DEXA as the reference standard. REMS is a promising adjunct, not a wholesale replacement. So if you hear DEXA is obsolete, that's marketing. That's not what the literature is saying.
00:26:58
Speaker
So let's land this plane, shall
Conclusion and Call to Action
00:27:00
Speaker
we? In summary... DEXA is still the gold standard. It is widely available. It's heavily researched. It's guideline anchored.
00:27:08
Speaker
And it's very good at what it does. It measures cross-section BMD at certain sites, and it helps to estimate fracture risk. It's not perfect, but it is the backbone, sorry for the pun, of your osteoporosis diagnosis.
00:27:24
Speaker
Whereas REMS is newer It's, yes, radiation-free, ultrasound-based technology. It has a strong correlation to DEXA. It has promising data on diagnostic ay accuracy and fracture prediction. And it has a potential advantage in situations where DEXA struggles, right? Especially when you've got a bunch of stuff going on in your spine.
00:27:47
Speaker
So the question is not which team are you on, but given my body, my risk factors, my access, and my budget, which tool or combination of tools gives me the most useful, actionable information?
00:28:00
Speaker
And in most mainstream clinical situations, that's still going to be your DEXA. In some cases, adding ah yet REMS or using REMS can refine that picture, especially when the story that the DEXA is telling doesn't match the reality of your fractures or your spine.
00:28:17
Speaker
Now, as always, there are levers that actually change your fracture risk. And these are progressive strength training, loading appropriately,
00:28:29
Speaker
working on fall prevention, and medical management sometimes when it's indicated. The scan is just there to help you pull these levers more intelligently, right? So the choice you have is just to give you information around which of these levers are the right ones for you to pull for your situations.
00:28:55
Speaker
Okay, hopefully you found this helpful and it helped you understand the difference between DEXA and REMS. Thank you so much for listening. If you enjoyed this episode, please forward it to possibly a friend who's looking at a DEXA score and rubbing their heads and saying, what the heck is all of this?
00:29:11
Speaker
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00:29:32
Speaker
So you got an extra day to get in there and grab some of those tutorials for yourself. All right, we'll see you in two weeks.