Accuracy of DEXA Scans

Posted by njhornung @normahorn, Mar 9 7:07pm

I am guessing that I am not the only one facing a medication decision based on one DEXA scan with no fractures. That raises the question as to how much reliance we should put on that single measurement. I trust that sites calibrate the instruments according to the manufacturer's specifications. But we read about the importance of proper positioning. I was only asked to lie on a table with no special consideration of position. Does improper position make bones appear denser or less dense? Or is the effect minimal?

Remember the old weight charts that had ideal weight ranges by height and bone structure? Does DEXA factor in bone structure when calculating density. Obviously, there is less bone for the x-rays to penetrate for a fine-boned person than for a heavy-boned one. That could be interpreted has having less bone mineral density which may not be the case.

Any insight or other pertinent questions?

Interested in more discussions like this? Go to the Osteoporosis & Bone Health Support Group.

My doc mentioned the importance of positioning in terms of having the same "area of interest" scanned each time. Comparisons of scans over time are important so consistency in area of interest is necessary.


I’ve had the same question about smaller bones scoring lower numbers. This article says they’ve decided it doesn’t matter much (looks at men’s and women’s bone) when considering fracture risk.
Using the Same Bone Density Reference Database for Men and Women Provides a Simpler Estimation of Fracture Risk

The International Atomic Energy Agency has a publication all about the DXA bone scan:
This states that there are definite differences in the size and bone density of men and women and some populations, Asian is mentioned. It says that DXA looks at only 2 parameters and cannot determine a difference between a thicker less-dense bone and a thinner high-density bone.
It also states there can be about an 8% difference in scores from different machines.

I’ve felt unsure of my DXA scores as I have smaller wrist bones than many women of my height. Also because I don’t know anyone who has broken their hip, I’m 70 yo. My mother (osteoporosis) and 2 older sisters (both with osteopenia) have never broken a hip. Although my mother had some compression spinal fractures in her later years.

I did finally decide to start bone density treatment - which is a good thing because right at that same time I was diagnosed with breast cancer. Some of the bone density treatments can harden the bone against metastasis (and bone is one of the first places BC will often move to). So I see it doing double duty, increasing bone and deterring cancer.


The logical inference, if the software does not adequately compensate for bone structure (fine, moderata, heavy). is that some fine-boned people diagnosed with osteoporosis may actually have osteopenia and some heavy boned people diagnosed with osteopenia may actually have osteoporosis. Both may not be getting the treatment that is right for them.

BTW, I noticed that the AEC article is from 2010 but the basic science has not changed.


I too have questioned my tscore since I'm of short stature and low weight. Dr. McCormick recommends asking for your trabecular bone score that uses a program that connects to the dexa scan. This measures your bone quality instead of just having your bone quantity which has reported my tscore of -3.4 of lumbar spine. He also recommends getting bloodwork for your bone markers (CTX & P1NP) before and during any treatment to determine the best medicine for your bones. Ctx measures how you are breaking bone while P1NP measures how much your bones are building. Check out his latest book Great Bones. It is filled with valuable information because most endocrinologist don't dive into all the possible causes of your low bone density. I currently am seeing a functional medicine aprn as well that has done more bloodwork that the endocrinologist did not order.


The logical inference, if the software does not adequately compensate for bone structure (fine, moderata, heavy). is that some fine-boned people diagnosed with osteoporosis may actually have osteopenia and some heavy boned people diagnosed with osteopenia may actually have osteoporosis. Both may not be getting the treatment that is right for them.

BTW, I noticed that the AEC article is from 2010 but the basic science has not changed.

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I agree with your inference - I can’t quite make out how they came to their conclusion that one score fits all. Did you read the NIH link? - I’m not positive I caught all the info. It seemed they put more focus on whether the standard deviation, based on a 30 yo white female, could be applied to men (with larger bone mass). It also seemed that they recognized that the individual bone mass was different - I can’t help but feel it was implied that the physician would make a clinical decision on what “normal” was and adjust their treatment plan accordingly. Normal meaning an average sized white female - and if the patient is larger, smaller, different race, the score would be expected to be different. But I’m afraid that is not what is happening in a typical PCP or endocrinologist office.

The FRAX score is usually used as part of decision making for BMD treatment.
I find this a rather simple tool. It is also dependent on knowing whether there has been a previous fracture. My mother had undiagnosed spinal compression fractures that did not get diagnosed until the pain increased. Perhaps the tool is meant to capture clinically relevant fractures only.

My FRAX score barely met criteria for treatment. And based on my thinner bone, I may have had only osteopenia not osteoporosis. But, for me, the breast cancer metastasis issue is now a factor. And it pushes me over into taking Reclast infusions- at least until the risk of invasive cancer is lower.



I'm at the exact same place as you Norma. I had 2 scans, one in Dec 2022 without TBS VFA(Vertebral Fracture Assessment) & my most recent, Feb of 24, with TBS/VFA.
Second scan performed in a different facility. It's, in my mind, not that I doubt there's a system in place that qualifies the need, but is that system accurate? The list of variables is endless and not cemented unless you've already fractured! Variables such as in machines, positions, technicians, health history, contridicting studies, new data, on and on! I keep reading, watching videos & there's not enough time in the day. Sooner or later it affects your well-being & you need to decide. I've vacillated for over a year. I see my Rheum in April and will make that decision then. Stressed since diagnosis 2022!

Information chgs in time, I get it, but I think the *summary below is still worth noting (could not access articles) and the *article on the stats gathered for use of meds according to "their" research. It is, no doubt, what we ourselves feel most at peace with. Yet, one thing for sure, "Harms from overdiagnosis—Being labelled as at risk of fracture imposes a psychological burden.!" Since we live longer are these the necessary tools, if all else failed, and at the same time I read hip fractures in Finland have leveled off, why? What I am positive about, is mindfulness, practice to incorporate the whole body approach to this dilema.

Osteoporosis: How effective are the medications used to prevent bone fractures? - - NCBI Bookshelf

Recent DXA VFA, you'll have to click to enlarge and swipe to right for added rept.


Summary would not allow me to photo or share link so copy/paste 😊


I wish there was more guidance on answering questions for the FRAX score. I changed mine drastically by how I answered one question.

In my 20's, I broke a finger playing touch football when I jumped up, but not high enough. to catch a football. Only a splint was needed. (Of course it was the middle finger that was splinted.) Then maybe 25 years ago, I slipped on thick ice and fell, breaking my ankle. It was a clean break and only a cast was needed. Include or not for the FRAX? What a difference including/not including those makes.

Currently, my intention is to hold off starting a lifetime of medication until I get another DEXA. I am not obsessing over my condition; treating it the same as my cll and possible brain aneurysm. Going on with my life with monitoring on a semi-annual/annual basis.


Lol, Norma, good for picking the right finger!!!

Exactly, there are so many variables, and of course physical activity can cause injuries. I'm concerned with my hip, so I need to decide.

BTW, the price of this test was crazy high, I was shocked, nearly $900.


I think we would all want the DXA test to be very accurate with no complicating factors, at least before we've had the test. Once we've had the test and if we have a bad score we want complicating factors to explain away that bad score so that we can have some hope that we really don't have that bone loss or that maybe it isn't as bad as it seems. At least it was that way for myself.
I paid to have Lani Simpson review my scans because I had lost so much bone between 2 of the scans. Unfortunately she said the scans were good and my bone density was dropping rapidly. At least I knew for sure or as close to sure as I was going to get that I was declining in bone density and that my efforts so far have not stopped that. Note: I have had 5 scans over the past 4 years and the last 4 were on the same machine and with the same technician so I've got a pretty clear view of how I'm doing DXA wise.

My bone density has declined to a worst of -4.1 t-score in the spine at my most recent scan. I have not fractured unless there are silent thoracic fractures. I wish DXA scans were better with no inconsistencies or worries about accuracy. I wish all the factors were known about how bone density and bone quality and bone strength and bone mass and yet unknown factors effected the risk of fracturing. BTW my TBS score is also bad. Not sure which TBS numbers are most relevant but I ranged from L1 0.984 to L4 at 1.305. My TBS scores did actually improve slightly. Still no fractures and plenty of opportunity for them. It is all frustratingly imperfect.
Still so glad I haven't fractured.

I think we have to be aware of the imperfections in all this and analyze the tests value and accuracy as best we can. And of course get the best help we can to help us sort this out. Despite the issues surrounding DXA scans I see them as very useful and not to be ignored. It's a test that provides useful information. Unfortunately many, maybe most docs do not know how to make best use of that information. It is up to each of us to try to do that. No matter what all the other factors are rapidly decreasing bone density or a very low steady state bone density are not good.

Despite doing the full set of blood tests that Lani recommended I/we could find no underlying explanation for my high rate of decline in density. A decline I could not stop despite dietary changes and following good resistance training and other exercise protocols. I chose to take Evenity and have had 5 shots so far. Fingers crossed. I'm still working on the dietary and exercise angles more than ever but I'm hoping this med makes a big difference.

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