# DEXA (DEXA)

A whole-body scan that measures fat, lean and bone separately, the reference consumer measure of body composition; the anchor that corrects your scale’s body fat.

Type: technique · Unit: %, kg, g/cm² · Domain: Body Composition · Accuracy: Laboratory · Importance: Supporting

Also called: dual-energy X-ray absorptiometry, body composition scan, bone density scan, DXA

## In one sentence

A whole-body scan that measures fat, lean tissue and bone separately, for the whole body and for each region, and is the reference measure of body composition a member can get.

## How it works, in a sentence

Two X-ray beams of different energies pass through you; bone, lean tissue and fat absorb them differently, and from the difference the scanner builds a map of what you are made of, region by region.

## Strengths

Precision: on the same machine, under the same conditions, a repeat scan agrees to within about 1 to 2 points of body fat, so real change of a kilogram of fat shows (Nana 2015). Detail: arms, legs and trunk are measured separately, which gives the appendicular skeletal muscle index and, on some systems, an estimate of the fat around the organs. And bone: the same session measures bone mineral density, the test doctors use for bone health.

## Weaknesses

It is still an estimate with assumptions. Hydration moves the lean figure, so a scan after a hard session or a big meal differs from a fasted morning scan; the best-practice protocol asks for rested, overnight-fasted, minimal clothing and standard positioning, and reports which machine and software were used (Nana 2015). Different makers' machines read a point or two apart (GE Lunar systems read about a point and a half differently from the Hologic systems the US reference curves were measured on; Imboden 2017), so repeat scans belong on the same machine. It costs money and a visit.

## Radiation

Very low. A whole-body scan delivers a few microsieverts, far less than a chest X-ray and about what a day of ordinary background radiation gives; the reviews of dose in bone imaging describe DEXA doses as very low and note that, as with any X-ray, each scan should have a reason (Damilakis 2010). Not during pregnancy.

## How Vitality Tracker uses it

As the anchor that corrects your scale. Your scale's body fat is a biased estimate; a DEXA scan tells VT the size of that bias for you, and from then on the scale's daily trend sits on a calibrated level (the DEXA correction). The regional values give your appendicular skeletal muscle index; the body-fat percentile is computed from the corrected value. One scan a year, or at the start and end of a plan, is enough; the scale does the daily work in between.

## Getting one in New Zealand

Private body-composition scanning is available in the main centers without a referral; a bone-density scan is a medical test your doctor orders. Bring back the full report, which VT reads: total body fat percent, fat mass, lean mass, bone mineral content, the regional values, and the visceral fat estimate if the system reports one. Book the morning, fasted, after the toilet, in light clothing, and use the same provider next time.

## Sources

1. Nana A, Slater GJ, Stewart AD, Burke LM. Methodology review: using dual-energy X-ray absorptiometry (DXA) for the assessment of body composition in athletes and active people. Int J Sport Nutr Exerc Metab 2015;25:198–215. [doi:10.1123/ijsnem.2013-0228](https://doi.org/10.1123/ijsnem.2013-0228)
2. Damilakis J, Adams JE, Guglielmi G, Link TM. Radiation exposure in X-ray-based imaging techniques used in osteoporosis. Eur Radiol 2010;20:2707–14. [doi:10.1007/s00330-010-1845-0](https://doi.org/10.1007/s00330-010-1845-0)
3. Imboden MT, et al. Reference standards for body fat measures using GE dual energy X-ray absorptiometry in Caucasian adults. PLoS One 2017;12:e0175110. [doi:10.1371/journal.pone.0175110](https://doi.org/10.1371/journal.pone.0175110).

## Related

- [Body fat](https://vitalitytracker.app/knowledge/body-fat)
- [Body-fat percentile](https://vitalitytracker.app/knowledge/body-fat-percentile)
- [Appendicular skeletal muscle index](https://vitalitytracker.app/knowledge/asmi)
- [Bone mass](https://vitalitytracker.app/knowledge/bone-mass)
- [Bioimpedance: the smart scale](https://vitalitytracker.app/knowledge/bioimpedance)

Reviewed October 2026 · v1

Source: https://vitalitytracker.app/knowledge/dexa