1. < Osteoporosis & Bone Health
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DEXA machines are not all the same!

Posted by njx58 @njx58, Sep 16 6:09pm

I had heard this, and AI confirms:

Numerical Differences: Hologic DXA scanners typically measure lower Bone Mineral Density (BMD) and T-scores than GE Lunar DXA systems at major sites like the lumbar spine and femoral neck.

Clinical Impact: Because Hologic readings trend lower, studies show that up to 50% of patients diagnosed with osteoporosis on a Hologic machine may fall into a different diagnostic or fracture-risk category if scanned on a Lunar device.

Tracking Progress: You cannot reliably compare serial T-scores or BMD changes over time if you switch between a Hologic and a Lunar machine. Cross-calibration formulas exist, but consistency at the same facility using the same machine brand is crucial.

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

Profile picture for oknowwhatpixie
oknowwhatpixie | @oknowwhatpixie | Sep 16 7:51pm

Yes, this I experienced myself. Definitely made me question my diagnosis.
Lumbar Spine
10/2023 TScore -2.7 (0.855) GE Lunar
01/2025 TScore -3.5 (0.659) Hologic
11.7% BMD Change (attributing to different machine)
No way I lost that much BMD in 14 months, especially when during 2024 I had all the tests run to determine no other reason for bone loss other than menopause.

Hologic spinal bone mineral density (BMD) values and T-scores are systematically lower—typically 11% to 20% lower—than those measured on GE Lunar systems.

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summera1 | @summera1 | Sep 17 8:21am

So, does this mean if I had DEXA on Hologic (-3.9), that I am taking Tymlos when I do not need it?
Ai said..... The slight difference between -3.9 and -3.3 is purely due to the fact that Lunar and Hologic use different reference groups and math formulas to calculate their scores—not because your bones are physically different.

I just asked Ai it said When we plug your actual BMD of 0.631 g/cm² into the cross-calibration formulas, here is how the numbers shift:Your Hologic Results: BMD of 0.631 g/cm² | T-score of -3.9Estimated GE Lunar Results (L4 Specific): BMD of 0.803 g/cm² | Estimated T-score of approx. -3.3Estimated GE Lunar Results (General Spine): BMD of 0.729 g/cm² | Estimated T-score of approx. -3.9Why You Still Have Osteoporosis. While an estimated Lunar T-score of -3.3 looks slightly "better" than a Hologic T-score of -3.9, it is crucial to look at where both numbers fall relative to the World Health Organization (WHO) diagnostic categories:Normal Bone Density: -1.0 or higher Osteopenia (Low Bone Mass): Between -1.0 and -2.5Osteoporosis: -2.5 or lower because both your actual Hologic T-score (-3.9) and your estimated Lunar T-score (-3.3 to -3.9) are significantly below the -2.5 threshold, your bone density is firmly in the osteoporosis range on both machines. The slight difference between -3.9 and -3.3 is purely due to the fact that Lunar and Hologic use different reference groups and math formulas to calculate their scores—not because your bones are physically different.

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oknowwhatpixie | @oknowwhatpixie | Sep 17 9:10am
In reply to @summera1 "So, does this mean if I had DEXA on Hologic (-3.9), that I am taking Tymlos..." + (show)
Profile picture for summera1 @summera1

So, does this mean if I had DEXA on Hologic (-3.9), that I am taking Tymlos when I do not need it?
Ai said..... The slight difference between -3.9 and -3.3 is purely due to the fact that Lunar and Hologic use different reference groups and math formulas to calculate their scores—not because your bones are physically different.

I just asked Ai it said When we plug your actual BMD of 0.631 g/cm² into the cross-calibration formulas, here is how the numbers shift:Your Hologic Results: BMD of 0.631 g/cm² | T-score of -3.9Estimated GE Lunar Results (L4 Specific): BMD of 0.803 g/cm² | Estimated T-score of approx. -3.3Estimated GE Lunar Results (General Spine): BMD of 0.729 g/cm² | Estimated T-score of approx. -3.9Why You Still Have Osteoporosis. While an estimated Lunar T-score of -3.3 looks slightly "better" than a Hologic T-score of -3.9, it is crucial to look at where both numbers fall relative to the World Health Organization (WHO) diagnostic categories:Normal Bone Density: -1.0 or higher Osteopenia (Low Bone Mass): Between -1.0 and -2.5Osteoporosis: -2.5 or lower because both your actual Hologic T-score (-3.9) and your estimated Lunar T-score (-3.3 to -3.9) are significantly below the -2.5 threshold, your bone density is firmly in the osteoporosis range on both machines. The slight difference between -3.9 and -3.3 is purely due to the fact that Lunar and Hologic use different reference groups and math formulas to calculate their scores—not because your bones are physically different.

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@summera1

I think of it like this that we have bone loss, and need to address it.

Theses machines while being the so call gold standard, can scare many people into starting medication when they might not yet need it. Add to it the lack of specialists in this area and its no wonder many question what to do next and feel concerned about the medication route. And then the overuse of prolia without explaining to patients the risks and the plan of following up with another medication to lock in gains.

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njx58 | @njx58 | Sep 17 9:51am
In reply to @summera1 "So, does this mean if I had DEXA on Hologic (-3.9), that I am taking Tymlos..." + (show)
Profile picture for summera1 @summera1

So, does this mean if I had DEXA on Hologic (-3.9), that I am taking Tymlos when I do not need it?
Ai said..... The slight difference between -3.9 and -3.3 is purely due to the fact that Lunar and Hologic use different reference groups and math formulas to calculate their scores—not because your bones are physically different.

I just asked Ai it said When we plug your actual BMD of 0.631 g/cm² into the cross-calibration formulas, here is how the numbers shift:Your Hologic Results: BMD of 0.631 g/cm² | T-score of -3.9Estimated GE Lunar Results (L4 Specific): BMD of 0.803 g/cm² | Estimated T-score of approx. -3.3Estimated GE Lunar Results (General Spine): BMD of 0.729 g/cm² | Estimated T-score of approx. -3.9Why You Still Have Osteoporosis. While an estimated Lunar T-score of -3.3 looks slightly "better" than a Hologic T-score of -3.9, it is crucial to look at where both numbers fall relative to the World Health Organization (WHO) diagnostic categories:Normal Bone Density: -1.0 or higher Osteopenia (Low Bone Mass): Between -1.0 and -2.5Osteoporosis: -2.5 or lower because both your actual Hologic T-score (-3.9) and your estimated Lunar T-score (-3.3 to -3.9) are significantly below the -2.5 threshold, your bone density is firmly in the osteoporosis range on both machines. The slight difference between -3.9 and -3.3 is purely due to the fact that Lunar and Hologic use different reference groups and math formulas to calculate their scores—not because your bones are physically different.

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@summera1 -3.3 is still a poor score. -3.9 is a really poor score. What would be questionable is if you had -3.0 on one machine and -2.5 on another, because -2.5 is not an automatic "must take meds" situation.

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boneoptimist | @boneoptimist | Sep 17 12:45pm

And even tho the tests I've had were on the same machine with the same technician, the area on the femoral neck was slightly larger on the current test than the previous test, making it look like a minor loss, but my rheumatologist caught the difference, did the math and said I had a 5.7% gain not a slight loss. Go figure. I think that as long as your T scores are trending down and your bone density is stable or trending up, and your TBS score is trending up, then you keep rocking it, carry on you Bone Warriors!

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alidamc | @alidamc | Sep 18 12:23pm

I wonder how I can find out which machine was used on me? It really doesn’t matter, I guess, since I break bones and don’t even realize it except fot some pain. When I broke my rib, I thought I just sprained a muscle. Still it would be nice to know.

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oknowwhatpixie | @oknowwhatpixie | Sep 18 4:54pm
In reply to @alidamc "I wonder how I can find out which machine was used on me? It really doesn’t..." + (show)
Profile picture for alidamc @alidamc

I wonder how I can find out which machine was used on me? It really doesn’t matter, I guess, since I break bones and don’t even realize it except fot some pain. When I broke my rib, I thought I just sprained a muscle. Still it would be nice to know.

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@alidamc
Your DEXA report should note the machine that was used.

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