Ein DEXA-Scan erfasst Knochen und Körperfett in einem einzigen Durchgang mit niedriger Strahlendosis: Wie dicht Ihre Knochen sind und wie sich Ihr Gewicht in Fett und Muskulatur aufteilt. Er erkennt das Fett und die Muskulatur, die eine Waage nicht unterscheiden kann, sowie den Ort der Fettablagerung. Für die Knochengesundheit ist er der Referenztest: Er definiert Osteoporose anhand des T-Werts, und eine geringere Knochendichte bedeutet ein höheres Frakturrisiko.
Er misst auch Körperfett und fettfreie Masse genau genug, um echte Veränderungen über Monate hinweg zu verfolgen. Diese Zahlen haben nur dann einen Sinn, wenn sie am selben Scanner abgelesen und über die Zeit verfolgt werden.
What It Is
DEXA, written more precisely as DXA, is dual-energy X-ray absorptiometry: one scan that measures both bone density and how your body's weight breaks down into fat and muscle.
It is the reference standard for diagnosing osteoporosis, and one of the most accurate body-composition measurements an ordinary person can reach. A bathroom scale gives one number for the whole body. BMI counts a kilogram of muscle and a kilogram of fat the same. A lean, muscular person can read as overweight, while someone at a normal weight can carry central fat that raises risk. DEXA measures the fat and muscle separately, and where the fat sits.
How It Works
The scan sends two X-ray beams of different energies through you. Bone, fat, and lean soft tissue each absorb the two energies by different amounts. The machine reads the absorption and works out how much of each the beam crossed.
You lie still on a padded, open table for a few minutes while an arm passes over you. Nothing touches you, and there is no tunnel.
For bone, the beam measures bone mineral density, usually at the hip and the lumbar spine, the two sites where a fracture matters most. For body composition, a whole-body scan splits weight into three parts: fat, lean soft tissue, and bone mineral. It reports them whole-body and region by region, so arms, legs, and trunk read separately.
What The Numbers Mean
Bone comes back as two comparisons, a T-score and a Z-score. The T-score compares your bone density to a healthy young adult at peak bone mass, and the diagnosis is built on it.
At or below -2.5 is osteoporosis. Between -1 and -2.5 is low bone mass. Above -1 is normal.
The Z-score compares you to other people of your own age and sex. It is the more useful reading in younger adults and children, where a score well below the age-matched average points to an underlying cause worth investigating.
Body-composition numbers have no single diagnostic cutoff the way the T-score does. Their value is in the parts and the trend. A whole-body scan reports total fat, its split against lean tissue, limb muscle, and a visceral-fat estimate: each read against your own baseline.
What It Shows
Bone results rest on large pooled studies and the standard used everywhere to diagnose osteoporosis. Several body-composition results are validation studies and cross-sectional snapshots. They show DEXA measures fat and muscle accurately. They do not show that changing those numbers lowers your future risk.
On bone, DEXA is the reference. The T-score comes straight from DXA, and the lower the density, the higher the fracture risk. Modern DXA also reads a second bone number from the same spine image, the trabecular bone score. It grades bone texture and adds fracture-risk information beyond density alone.
On body composition, DEXA reads fat and lean tissue directly. Its visceral-fat estimate lines up closely with a CT scan. It is also one of the standard tools for confirming low muscle quantity, measured as appendicular lean mass.
The Research & Studies
Everything here is based on the research we have collected and checked, sorted into groups and ordered with the strongest evidence first. Click any claim to open the studies behind it.
Measurement And Diagnosis
Osteoporosis is defined by a DEXA T-score at or below -2.5
The number used to diagnose osteoporosis, the T-score, comes from a DXA scan. A T-score of -2.5 or lower means osteoporosis, and DXA of the hip and spine is the test that standard is based on.
The World Health Organization diagnostic thresholds, set from bone mineral density measured by DXA, define osteoporosis as a bone density 2.5 or more standard deviations below the young-adult mean, a T-score at or below -2.5, with the range from -1 to -2.5 termed low bone mass. DXA of the hip and spine is the measurement these thresholds are built on, which is why it is treated as the reference standard for diagnosis. The T-score is a statistical comparison to a young-adult reference, not a direct measure of bone strength, and diagnosis and treatment weigh it alongside age, previous fractures and other risk factors.
The study · 1
Kanis et al., The diagnosis of osteoporosis · J Bone Miner Res 1994;9(8):1137-41
DEXA body fat tracks the lab criterion model within about two percentage points
DXA measures body fat about as well as the best laboratory method available, within roughly two percentage points, though it reads a little low in very lean people.
In 152 healthy adults aged 18 to 59, DXA percent body fat tracked the four-compartment criterion model closely (r-squared 0.952, standard error of estimate 1.6 percent fat), though DXA read about 1.8 percentage points lower on average (18.9 versus 20.7 percent) and progressively underestimated fat in leaner people. What could explain it instead: The four-compartment reference model carries its own measurement error, and beam-hardening from differences in body thickness can bias DXA, so part of the disagreement reflects the limits of both methods, not DXA alone.. Agreement is close but not exact, and the small bias means DXA is best for tracking your own change over time, not for pinning down a single true percentage.
The study · 1
Van Der Ploeg et al., Percent body fat via DEXA: comparison with a four-compartment model · J Appl Physiol 2003;94(2):499-506
DEXA appendicular lean mass is a standard confirmation of sarcopenia
When clinicians diagnose age-related muscle loss, called sarcopenia, DXA is one of the standard tools they use to confirm how much muscle a person actually has.
The 2019 European Working Group on Sarcopenia in Older People consensus lists DXA-measured appendicular lean mass, adjusted for height, as one of the recommended ways to confirm the low muscle quantity that defines sarcopenia, used alongside a measure of muscle strength. DXA quantifies how much lean tissue is present, not its quality or function, so it sits within a diagnosis that also requires a strength or performance test.
The study · 1
Cruz-Jentoft et al., Sarcopenia: revised European consensus on definition and diagnosis (EWGSOP2) · Age Ageing 2019;48(1):16-31
DEXA visceral fat matches a CT scan closely, r-squared 0.957
DXA can estimate the fat packed around your organs, the visceral fat that matters most for metabolic health, and it lines up closely with a CT scan while using far less radiation.
In 124 adults aged 18 to 90 scanned by both methods within an hour, automated DXA visceral fat agreed closely with abdominal CT, the reference standard (r-squared 0.957 combined), and the authors concluded DXA can measure visceral fat precisely in both men and women at very low radiation. What could explain it instead: CT, the reference method, carries its own measurement error, and DXA estimates a volume from a two-dimensional scan, so some of the scatter between them reflects the limits of both techniques.. Agreement was close on average but the individual limits of agreement were fairly wide, so a single DXA visceral-fat number is better read as a trend over time than as an exact volume.
The study · 1
Kaul et al., Dual-energy X-ray absorptiometry for quantification of visceral fat · Obesity (Silver Spring) 2012;20(6):1313-8
Progress Markers
Each SD drop in bone density carries about 1.5 times the fracture risk
The lower your DXA bone-density score, the higher your fracture risk, in a steady gradient. Each one-step drop in density raised fracture risk by roughly half, and measuring at the hip predicted hip fractures best.
In a meta-analysis of 11 prospective cohorts with about 90,000 person-years of follow-up and more than 2,000 fractures, each one standard deviation fall in bone mineral density carried a relative risk of about 1.5 (95% CI 1.4 to 1.6) for fracture, rising to 2.3 (1.9 to 2.8) for spine measurement predicting vertebral fracture and 2.6 (2.0 to 3.5) for hip measurement predicting hip fracture. Bone density predicts fracture risk across a population but cannot identify which individual will fracture, and the authors did not recommend mass screening on density alone.
Who this may not transfer to:The prospective cohorts pooled here were of women. The same density-to-fracture gradient has since been documented in men, though this meta-analysis itself did not measure it, so the exact figures are from women.
The study · 1
Marshall et al., Meta-analysis of how well measures of bone mineral density predict occurrence of osteoporotic fractures · BMJ 1996;312(7041):1254-9
Each SD drop in trabecular bone score carries about 1.4 times the fracture risk, independent of bone density
Modern DXA reads a second bone number from the spine scan, the trabecular bone score, which grades bone texture. Each one-step fall in it carried about 1.4 times the fracture risk, and it still predicted fractures after accounting for bone density, so it tells you something density alone does not.
In an individual-level meta-analysis of 17,809 men and women across 14 prospective cohorts followed a mean of 6.7 years, the trabecular bone score, a texture measure read from the same lumbar-spine DXA image, carried a gradient of risk of 1.44 (95% CI 1.35 to 1.53) per standard deviation for major osteoporotic fracture, and 1.32 (95% CI 1.24 to 1.41) after adjustment for the FRAX 10-year fracture probability, so it added fracture-risk information beyond bone density itself. The gradient was similar in men and women. The trabecular bone score is an addition to bone density and a fracture-risk calculator, not a replacement, and how much it should shift a clinical decision is still being worked out.
Who this may not transfer to:The pooled cohorts included both men and women and the gradient of risk was similar in each, so the finding reads across the sexes.
The study · 1
McCloskey et al., A meta-analysis of trabecular bone score in fracture risk prediction and its relationship to FRAX · J Bone Miner Res 2016;31(5):940-8
Low muscle mass tracks with a higher death rate in older men
In large groups of older men followed over years, those with the muscle loss that DXA helps identify tended to die at higher rates than those without it.
Across pooled population-based cohorts of older men, sarcopenia defined by recent criteria, which include low DXA-measured muscle mass, was associated with higher all-cause mortality over follow-up, with the size of the association varying by which definition was applied. What could explain it instead: Reverse causation and underlying illness. Serious disease both wastes muscle and raises the risk of death, so part of the association reflects existing illness, not low muscle mass causing death.. This analysis was in men only, the strength of the association depended on the definition used, and it is observational, not a trial.
Who this may not transfer to:Measured in men only. Age-related muscle loss tracks with mortality in women in other cohorts, but this analysis did not include women, so the size of the association here should not be read across to them.
The study · 1
Westbury et al., Recent sarcopenia definitions: prevalence, agreement and mortality associations among men · J Cachexia Sarcopenia Muscle 2023;14(1):565-575
Visceral fat tracks cardiometabolic risk more tightly than overall body fat
The visceral fat DXA measures lines up with heart and metabolic risk factors more tightly than overall body fat does, and a little better than a tape-measure waist.
In 4,831 Australian adults aged 45 to 69, DXA-measured central fat, including abdominal visceral adipose tissue, showed stronger associations with metabolic syndrome and cardiometabolic risk factors than overall-adiposity measures, and DXA visceral fat was more strongly associated than waist circumference. What could explain it instead: Cross-sectional design and reverse causation. The scan and the risk factors were measured at the same time, so the data cannot show that visceral fat came first, and metabolic disease can itself change where fat is stored.. This was a cross-sectional snapshot, so it shows association at one point in time, not predicting future events, and the added value over a simple waist measurement was modest.
The study · 1
Zhu et al., DXA-derived versus standard anthropometric measures for predicting cardiometabolic risk in middle-aged Australian men and women · J Clin Densitom 2022;25(3):299-307
How it works
DEXA is precise, but scans compare only on the same machine
DXA is precise enough to track small real changes, but different machines do not read exactly alike, so repeat scans should be done on the same machine to compare fairly.
The International Society for Clinical Densitometry sets minimum precision standards for DXA and requires a cross-calibration study whenever a scanner is changed or replaced, and especially between manufacturers, because bone-density readings do not transfer directly from one machine to another. A change that looks meaningful can be machine drift instead, which is why it must exceed the scanner and technologist precision error before it counts.
For tracking bone or body composition, return to the same DXA machine each time. If you must switch, a result from a different scanner or manufacturer is not directly comparable without a cross-calibration.
The study · 1
Shepherd et al., Cross-calibration and minimum precision standards for dual-energy X-ray absorptiometry: the 2005 ISCD Official Positions · J Clin Densitom 2006;9(1):31-6
Three Limits On The Numbers
Three things change how far you should trust a DEXA number.
A change must clear the measurement error before it counts. A single reading carries some scanner and technologist error. A real change has to be bigger than that built-in error, the least-significant-change margin, before it means anything. So read the trend across a baseline and a repeat scan.
The sarcopenia cutoffs are still loosely drawn. DEXA measures how much lean tissue is present. It does not measure the tissue's quality or strength. Expert groups set the limb-muscle cutoff at different points, so a muscle-mass number is paired with a strength or performance test.
DEXA estimates visceral fat instead of measuring it directly. The fat around the organs is estimated from the trunk area of a flat, two-dimensional scan, whereas a CT slice measures an actual volume. On average the two agree. But for any one person the estimate can be well off, so a single visceral-fat number reads best as a trend.
How To Use It
Treat a scan as a baseline you return to. For bone, the clinician sets the retest interval from your starting score, your risk, and any treatment. Many people are rescanned every one to two years, sometimes longer when bone is stable. Bone changes slowly, so a year or two usually has to pass before a repeat shows a real difference.
For body composition, scan every few months to a year. That is often enough to see whether a change in training or eating is moving fat and muscle the way you want.
Who Gets The Most From It
Postmenopausal women and older adults gain the most. Bone loss and muscle loss are both common with age, and a bone result can change what a clinician does next. Anyone with a condition or a medication that thins bone has a clear reason to scan. A repeat scan also shows whether your own effort is working: weight-bearing and resistance training load the skeleton, and the number tracks whether that loading holds or builds bone. If a low reading points toward thin bone, the osteoporosis guide covers what rebuilds it and where the medications fit.
People tracking muscle and fat while training or losing weight get the second use. The scan separates the fat they are losing from the muscle they want to keep. If you are lifting to hold muscle as you lean out, DEXA shows whether it is working.
Go Deeper
- Grip strength, the strength test that pairs with a muscle-mass number.
- Protein and muscle, how much protein preserves muscle during weight loss.
- Muscle as an organ, why lean mass matters beyond movement.
- Self-measures hub, the other numbers you can track yourself.
Reading A DEXA Scan Well
Everything to be aware of is here, in one place. This practice suits most healthy people; a few situations call for real care.
A DEXA scan uses very little radiation, far less than a CT scan
A review of X-ray imaging used to assess the skeleton reports that radiation doses from DXA are very low, well below the 1 to 3 millisieverts delivered by CT-based bone methods, while noting that, as with any X-ray, each scan should be clinically justified. Very low is not none. DXA is generally avoided in pregnancy, and children are more sensitive to radiation than adults, so their scan protocols are adjusted to keep the dose down.Damilakis et al., Radiation exposure in X-ray-based imaging techniques used in osteoporosis
The radiation is very small
A DEXA scan uses a very low dose of radiation, far below a CT scan. The dose is not zero, so a scan is usually ordered with a specific bone or body-composition question in mind.
Avoided in pregnancy, and adjusted for children
The dose is low but not zero. DEXA is generally avoided in pregnancy, and children are more sensitive to radiation than adults, so their scan protocols are set to keep the dose down. Tell the clinic if you are or might be pregnant.
Compare scans on the same machine
Different DXA scanners, especially from different manufacturers, do not read exactly alike. To track a change, return to the same machine each time. A result from a different scanner is not directly comparable without a cross-calibration, so a difference between two clinics can come from the scanners themselves.
One input among several
A T-score or a body-composition number is one input that a clinician weighs alongside age, fracture history and medications. Nothing here is a reason to start, stop or change a medication.
Start slow, be smart, read the research, and consult a professional if you have any concerns. This is here to inform your choice, not make it for you.
Common Questions
What is a DEXA scan, and what does it measure?
A DEXA scan (dual-energy X-ray absorptiometry, or DXA) sends two low-dose X-ray beams at two energy levels through the body. From how much each beam is absorbed, it separates bone from fat and lean soft tissue. That lets one scan report bone mineral density, most often at the hip and spine. It also reports whole-body composition, how your weight splits into fat and muscle, including the visceral fat. You lie still on an open table for a couple of minutes and nothing touches you.
What does my T-score mean?
Your T-score sets your bone density against a healthy young adult's peak bone mass. A normal score sits above -1, low bone mass falls between -1 and -2.5, and -2.5 or lower is the diagnostic line for osteoporosis, the standard set from DXA. Risk rises steadily as the score falls: each one-standard-deviation drop carried about 1.5 times the fracture risk across pooled cohorts. In younger adults and children, the Z-score is the more useful reading. It compares you to others your own age and sex.
Is DEXA accurate for body fat, compared with a smart scale or BMI?
BMI cannot tell muscle from fat. Home bioimpedance scales estimate body fat indirectly from a small electrical current that shifts with hydration. DEXA measures fat and lean tissue directly. In a study of 152 adults, it tracked a four-compartment model, the laboratory reference, to within about two percentage points of body fat. It also reports the parts (arms, legs, trunk and the visceral fat) that a single scale number cannot. DEXA reads a little low in very lean people, so it is best for tracking your own change over time.
How much radiation does a DEXA scan use?
A very low dose, far below a CT scan. That low dose is one reason the same scan can be repeated to track a change. The dose is not zero, so a scan is usually ordered with a specific question in mind. DEXA is generally avoided in pregnancy, and children are scanned on dose-reduced protocols, because a child's tissue is more radiation-sensitive.
How often is it worth getting a DEXA scan?
For bone, the interval is a clinical decision, often every year or two, and longer when bone is holding steady. Bone remodels too slowly for a shorter gap to show a real change. For body composition, once or twice a year is enough to tell whether training or eating is shifting fat and muscle as intended.
Can I compare scans from different machines?
Not directly. Different DXA scanners, particularly from different manufacturers, do not read exactly alike, and the professional standards require a cross-calibration whenever the hardware changes. If your second scan is on a different machine, a shift in the number can come from the scanner itself. Returning to the same clinic and machine is the simplest way to be sure a change on the report is real.
Explore Related
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All 10 sources on this page independently checked and cross-referenced.
Thomas Dehli, Founder & Editor, Sacred Lotus
Sacred Lotus has published Chinese medicine reference material since 2001. Integrative pages are held to the same standard as the herb and formula library: cite the source, grade the claim at its real strength, and say where the research has not looked. This page is educational and it is not medical advice. Last reviewed and updated August 10, 2026.