DEXA Scans, Body Composition and Bone Density

What a DEXA scan is

DEXA (also written DXA) stands for dual-energy X-ray absorptiometry. MedlinePlus describes a bone density scan as a low-dose X-ray that measures calcium and other minerals in the bones. [1] The same type of machine can also estimate fat mass and lean mass for the whole body and its regions, which is what "body composition" DEXA reports. The two uses have very different evidence behind them, so this page keeps them apart.

Evidence labels: approved medicine, established, promising but limited, mixed, insufficient evidence, marketing claim. Bone density testing for osteoporosis in certain groups has established guideline support. DEXA body composition for tracking "aging" has insufficient evidence of benefit.

Bone density: what guidelines say

In its 2025 final statement, the US Preventive Services Task Force (USPSTF) recommends osteoporosis screening to prevent fractures in women 65 years or older (grade B) and in postmenopausal women younger than 65 who are at increased risk by clinical risk assessment (grade B). For men, it concluded that evidence is insufficient to assess the balance of benefits and harms (grade I). [2]

The USPSTF notes that the most commonly used test is central DXA, which uses low doses of radiation, that fracture risk is best predicted when density is measured at the site in question, and that bone density alone may not be the most useful predictor of fracture risk, especially in younger people. [2] The statement covers adults 40 and older without known osteoporosis or a prior fragility fracture, and does not cover people with secondary osteoporosis such as from long-term glucocorticoid use. [2]

The UK NHS says bone density scans use much less radiation than standard X-rays and are not recommended in pregnancy. It says results are usually used alongside a fracture risk assessment. [3] Its page was last reviewed in October 2022, with a review due in October 2025, so check for updates.

For daily-life bone health, see Bone Health, Osteoporosis and Aging and Osteoporosis and Bone Health.

Body composition: what a scan can and cannot tell you

Dual-energy X-ray scanning is one of three methods (with CT and MRI) that a 2026 critical review calls "reference" approaches for measuring muscle mass, but the same review says there is no consensus on a true gold standard, and that studies often report acquisition and analysis protocols in too little detail to compare. [4]

A review of DEXA body composition change in athletes found that many studies did not report precision error and that pre-scan standardization (such as fasting) varied. It recommended a standardized protocol before interpreting "meaningful" change. [5] That review was about athletes, so results may differ in older adults.

What this means in plain terms:

• Small changes between two scans may be within measurement error unless the same machine and conditions are used. Label: mixed for tracking change.


• We found no source in this review showing that DEXA fat or lean mass numbers in healthy adults improve outcomes if acted on. Proper evidence not found for health benefit of routine body composition scans (we checked PubMed and the guideline pages above).


• A "biological age" or "muscle age" figure from a scan is a marketing claim unless a validation study is cited. Functional tests such as grip strength and chair stands have stronger outcome data; see Functional Measures.

How to evaluate a scan offer

• Is it a medical bone density test ordered for a clear reason, or a package of body composition numbers?
• Which machine is used, and will repeat scans use the same one?
• What will change if the number is high or low?
• Does a seller link results to supplements or treatments? See Red Flags in Health Claims.