How the measurement actually works.
Every method for measuring body composition is a model of the body with assumptions baked in. DEXA's assumptions happen to be unusually good, and its errors are unusually well characterised. Here's what it does, where it's strong, and where it isn't.
Two energies, three tissues
DEXA stands for dual-energy X-ray absorptiometry. The scanner sends two X-ray beams of different energies through you and measures how much of each is absorbed on the way. Bone mineral, lean soft tissue, and fat each attenuate the two energies in a distinct ratio, so the difference between the two readings is enough to separate them pixel by pixel.
Because the measurement is spatial, you get a map rather than a single figure: fat and lean mass reported for each arm, each leg, and the trunk, with bone mineral density measured at the sites where fracture risk matters. That regional detail is what most other methods can't give you at any price.
The dose involved is small — on the order of a few microsieverts for a whole-body composition scan, which is a fraction of a chest radiograph and less than a transcontinental flight. It's still ionising radiation, which is why we don't scan during pregnancy and don't recommend scanning more often than the measurement warrants.
How it compares
Every method trades something. This is the honest ranking.
What we don't claim
A DEXA scan is not a diagnosis. We're a testing facility, not a medical practice: we measure carefully, explain what the numbers mean, and hand you a report you can take to a physician. If something in your results warrants clinical attention, we'll say so and tell you to go.
We also don't sell a "biological age." You can compute one from body composition data, and it makes a satisfying single number, but the inputs are the same measurements you're already getting and the conversion adds assumptions rather than information. We'd rather show you your lean mass percentile and let it mean what it means.
And no scan replaces bloodwork, blood pressure, or a conversation with your doctor. This is one layer — the structural one — of a picture that needs several.
How we keep your scans comparable
Daily calibration
The scanner is calibrated against a phantom every day it's in use, and results are logged so drift is visible before it affects anyone's numbers.
One machine, one protocol
All scans run on the same GE Lunar Prodigy with the same positioning routine. Comparing across machines or software versions introduces error you can't correct after the fact.
Manual region checks
A technician reviews the automatic region boundaries on every scan. This step is a large share of why repeat scans line up.
Consistent conditions
We ask you to come in similarly hydrated, similarly fed, and at a similar time of day. It sounds fussy. It's the difference between reading a real change and reading a glass of water.