A DEXA scan is a low-dose X-ray examination that can assess bone mineral density and body composition. A whole-body DEXA scan may measure body fat, lean mass and bone mineral content, providing more detailed information than body weight or BMI alone.
What is a DEXA scan?
DEXA stands for dual-energy X-ray absorptiometry. The formal medical abbreviation is DXA, although “DEXA scan” remains the more commonly searched term.
The scanner uses X-rays at two low-energy levels to distinguish between bone mineral, fat and lean soft tissue. The examination is non-invasive and painless. No injection or enclosed scanning tunnel is normally required.
The Hospital Authority describes DXA as a very-low-radiation examination used to measure bone mineral density, assess bone strength and estimate fracture risk.
What does a whole-body DEXA scan measure?
Depending on the equipment, software and scanning protocol, a DEXA whole-body scan may report:
Lean mass represents lean soft tissue and is commonly used as an estimate of muscle mass. However, DEXA does not directly measure muscle strength, endurance or physical performance.
Why have a DEXA scan?
Two people with the same weight and BMI can have very different proportions of fat, lean tissue and bone. A DEXA scan provides a more detailed breakdown of what the body is made of.
The results may be useful for:
A baseline scan can also make future comparisons more meaningful, especially when repeat examinations are performed under similar conditions on the same machine.
Can a whole-body DEXA scan diagnose osteoporosis?
A whole-body scan provides an overview of bone density, but it should not be treated as a complete osteoporosis diagnostic test.
When osteoporosis screening or diagnosis is the main purpose, dedicated measurements of the lumbar spine and hip are normally required. These are the recognised sites used to calculate diagnostic T-scores and assess fracture risk.
Patients booking a scan should therefore clarify whether they require body-composition analysis, whole-body bone data, dedicated hip and lumbar-spine measurements, or a combination of these examinations.
Who should consider a DEXA scan?
There is no fixed age at which every adult needs body-composition analysis. A scan may be considered by people undergoing structured weight loss, muscle-building, rehabilitation or long term health management.
For osteoporosis assessment, recommend DXA screening for women aged 65 or above and men aged 70 or above. Younger adults may also require testing if they have relevant risk factors, including:
Is a DEXA scan safe?
DEXA uses a very low radiation dose. The scan is generally quick and painless, taking from several minutes to around 20 minutes depending on the areas being examined.
Anyone who is or may be pregnant must inform the healthcare team before the examination. Recent contrast examinations, certain implanted objects and body size may also affect the scan or its interpretation.
DEXA scans in Central, Hong Kong
Hong Kong Imaging and Diagnostic Centre provides DEXA whole-body bone density and body-composition analysis in Central. Dedicated hip and lumbar-spine measurements may also be added where appropriate.
Results should be interpreted according to the individual’s age, medical history, health risks and purpose of examination. One figure should not be used in isolation to make a diagnosis or treatment decision.
