DEXA scan
The gold standard for measuring bone mineral density and one of the most accurate ways to assess body composition — more precise than popular bioimpedance scales.
Number of studies
1
Safety
High
Time to effects
Not applicable — DEXA is a diagnostic test, not an intervention.
Who it's for
Table of contents
TL;DR
The gold standard for measuring bone mineral density and one of the most accurate ways to assess body composition — more precise than popular bioimpedance scales.
- →The most accurate, widely available method for assessing bone mineral density
- →Precise body composition measurement, more accurate than home bioimpedance scales
- →Very low radiation dose, safe to repeat periodically
| Type of test | Dual-energy X-ray absorptiometry |
|---|---|
| Evidence level | Strong — the gold standard for osteoporosis diagnosis |
| Target group | Postmenopausal women, older adults, athletes monitoring body composition |
| Parameters measured | Bone mineral density (T-score, Z-score), fat and lean mass |
| Radiation dose | Very low, significantly lower than a standard chest X-ray |
| Status | A diagnostic test available at medical facilities and some fitness clubs |
Understand
Overview
DEXA (dual-energy X-ray absorptiometry) is an imaging test that uses two different X-ray energy levels to precisely measure bone mineral density and the distribution of fat and lean tissue in the body. It's regarded as the gold standard for osteoporosis diagnosis and one of the most accurate, widely available methods of assessing body composition.
In the context of bone health, DEXA allows calculation of the T-score, which compares a patient's bone density to the peak bone mass of young healthy adults, forming the basis of the clinical diagnosis of osteopenia or osteoporosis. In the context of body composition, DEXA distinguishes fat, muscle, and bone tissue in individual body regions with far greater accuracy than popular electrical bioimpedance scales, which are more susceptible to fluctuations in hydration.
Who can realistically benefit from this? Postmenopausal women and older adults as part of osteoporosis prevention, athletes and strength trainees wanting to precisely track changes in muscle and fat mass over time, and anyone wanting to verify a home bioimpedance scale result with a more accurate method.
Mechanism of action
A DEXA scan emits two X-ray beams at different energy levels, which are absorbed differently by tissues of different density — bone absorbs radiation more strongly than soft tissue, and fat and muscle tissue differ from each other in absorption in a way that can be mathematically separated. Analyzing the difference in attenuation of the two beams after passing through the body allows software to precisely calculate bone mineral density and the proportions of fat and lean tissue in a given body region.
The radiation dose in a DEXA scan is very low, significantly lower than a standard chest X-ray, which makes it safe to repeat periodically to monitor changes over time — a key advantage compared with a single, isolated measurement.
Emission of two radiation beams
The device emits X-rays at two different energy levels.
Differential absorption by tissues
Bone, fat, and muscle tissue absorb radiation to different degrees.
Mathematical separation of tissues
Analyzing the difference in attenuation of the two beams allows precise calculation of tissue composition.
Evidence: strong — based on 1 study in this database.
Benefits
Common myths
MythBioimpedance scales are just as accurate as DEXA.
FactBioimpedance scales estimate body composition indirectly based on electrical resistance and are far more susceptible to hydration fluctuations, while DEXA measures body composition directly, with higher repeatability.
MythA DEXA scan carries significant radiation risk.
FactThe radiation dose in a DEXA scan is very low, comparable to a fraction of the dose received during a several-hour airplane flight.
Practice
Frequently asked questions
For bone density assessment, repeating every 1–2 years is usually recommended depending on risk factors; for monitoring body composition, an interval of 3–6 months is often enough.
It's usually recommended to avoid calcium supplements on the day of the test and to mention any recent contrast-enhanced imaging, which can distort the result.
No — the scan is completely painless, non-invasive, and usually takes a few to several minutes.
Safety
Side effects & contraindications
Possible side effects
Contraindications
Pregnancy — due to X-ray exposure, though very low
Is it worth taking?
Who it's for
- Postmenopausal women and older adults as part of osteoporosis prevention
- Athletes and strength trainees wanting to precisely monitor body composition
Not for
- Pregnancy — due to X-ray exposure, though very low
Evidence
Worth knowing
The T-score compares a patient's bone density to the peak bone mass of young healthy adults and forms the basis of the clinical diagnosis of osteoporosis.
DEXA is one of the few methods that can assess the distribution of fat and muscle tissue separately for individual body regions (e.g. trunk and limbs).
Studies
Dual-energy X-ray absorptiometry remains the reference method for assessing bone mineral density and osteoporotic fracture risk in clinical practice.
Kanis JA, The Lancet, 2002
Diagnosis of osteoporosis and assessment of fracture risk
Strong evidenceKanis JA · The Lancet · 2002
A review of osteoporosis diagnostic methods, including the role of dual-energy X-ray absorptiometry as the reference method.
View studySources & bibliography
Citations are illustrative for this demo version and require full bibliographic verification by the editorial team before production publication.
Compare with similar entries
About the authors of this entry
Author
dr Piotr ZielińskiEndocrinologist
Piotr reviews content on hormones, metabolic health and supplement pharmacology.
131 publications on this site
Medical review
Julia WiśniewskaEditor, Neurohacking & Sleep
Julia writes about nootropics, chronobiology and recovery protocols.
45 publications on this site
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Comments (2)
- KW
Kasia W. 2 weeks ago
Very clearly explained, especially the interactions section — I hadn't seen it laid out this well anywhere else.
- MT
Marek T. a month ago
Are you planning to update this with the newest study from this year? I saw an interesting meta-analysis.