What is the difference between a DEXA scan and a REMS scan?
Here's the point
A DEXA scan uses a low dose of X-ray to measure bone mineral density at the hip and spine, and it's the long-established standard that generates your T-score. A REMS scan uses ultrasound instead of radiation to assess the same areas, comparing the echo signal to reference models to produce its own T-score (not directly interchangeable with a DEXA T-score) plus a separate "fragility score" reflecting tissue quality. REMS is newer, has less long-term data, and is best used alongside DEXA rather than replacing it, especially if you already have a DEXA history.
DEXA (dual-energy X-ray absorptiometry) works by passing two low-energy X-ray beams through your hip and spine. The machine calculates how much mineral sits in the beam's path and reports this as areal bone mineral density in grams per square centimetre. Your T-score then compares that number to the average peak density of a healthy young adult. DEXA has decades of research behind it and is the test most used to track bone density over time.
REMS (Radiofrequency Echographic Multi Spectrometry) takes a different approach. It uses ultrasound rather than X-ray, analysing the raw echo signal from your spine and hip against reference models. It reports its own T-score, which is not directly interchangeable with a DEXA T-score, along with a fragility score that looks at tissue quality rather than density alone. Because it involves no radiation, it can be repeated more often, and it isn't thrown off by things like arthritis or calcification the way a lumbar DEXA sometimes can be.
The trade-off is that REMS is newer technology, so there's less long-term outcome data behind it compared with DEXA. For that reason, it's best thought of as a helpful complement rather than a replacement. If you already have a series of DEXA scans, it makes sense to keep using DEXA so your results stay comparable over time, rather than switching tests partway through.
Whichever test you use, keep in mind that density alone doesn't tell the whole story. Two people can have identical scores and very different actual bone strength, depending on things like bone architecture and what's driving the number in the first place. A single scan is a useful data point, not the complete picture.
Know these words
A DEXA scan is a low-radiation X-ray test that measures how much mineral is in your hip and spine bones, giving you…
REMS is an ultrasound-based scan that estimates bone density and tissue quality at the spine and hip without using…
A T-score shows how your bone density compares to a healthy young adult, measured in standard deviations, and it's…
Trabecular Bone Score (TBS) is a measurement taken from your spine DEXA image that estimates how well-connected your…
Bone mineral density (BMD) measures how much mineral is packed into your bones, usually estimated with a DEXA scan,…
Least Significant Change (LSC) is the smallest change in a DEXA scan result that's big enough to count as real,…
How sure is this?
Graded Emerging Evidence: Promising research, but findings are still developing and may be primarily from laboratory or animal studies. Read each study with its grade in mind. One study is a piece of the picture, not the whole of it.
The lessons behind this answer
More on tests and numbers
A T-score compares your bone density to that of a healthy young adult, measured in standard deviations: -1.0 and above is normal, -1.0 to -2.5 is osteopenia, and -2.5 or below is osteoporosis. But it's just one snapshot of density — it doesn't capture bone quality, your fall risk, or your overall fracture probability, so it's worth tracking several other things alongside it and discussing them with your physician.
Read the full answer →Osteopenia and osteoporosis are both based on your DEXA T-score, just at different points on the same scale. A T-score between -1.0 and -2.5 is called osteopenia (lower-than-average bone mineral density), while -2.5 or below is called osteoporosis (more significant bone loss). They're not two different diseases — they're a continuum, and the cut-off points are statistical conventions used for research and reimbursement, not a biological cliff where something suddenly changes in your skeleton.
Read the full answer →A T-score compares your bone density to that of a healthy young adult at peak bone mass, and it's the number used to apply the standard categories of normal, osteopenia, or osteoporosis. A Z-score instead compares you to people of your own age and sex, which makes it the more appropriate number for anyone premenopausal, for men under 50, and for children, since a T-score can be misleading in those groups.
Read the full answer →For most people, the honest answer is every 1 to 2 years. DEXA machines have a built-in measurement error, and most facilities can't reliably detect a real change in bone density sooner than that — a small shift of 1-2% on your scan often just reflects machine noise, not actual bone loss or gain. Your physician can tell you the right interval for your specific situation.
Read the full answer →CTX and P1NP are blood tests that show how fast your bone remodeling is happening right now, rather than where your bone density stands. CTX reflects how quickly bone is being broken down, and P1NP reflects how quickly new bone is being built. Unlike a density scan, which takes a year or more to show change, these markers can shift within weeks to months, so they're useful for tracking your own trend over time.
Read the full answer →Have a question that isn't here? Ask us at your next visit, or ask our AI bone health advisor.
Education only, not medical advice. Decisions about tests, medications and treatment belong with your own doctor. OsteoStrong does not diagnose, treat or cure any disease.
