DEXA Scan vs Bone Density Scan: What’s the Difference?
- 1 day ago
- 3 min read
If you’ve been told you need a “DEXA scan,” you may be surprised to learn there are actually two different types of scans people commonly refer to under the same name.
One is a diagnostic bone density scan (BMD) used to assess bone health and screen for conditions such as osteopenia and osteoporosis. The other is a body composition DEXA scan, designed to assess muscle mass, body fat and body composition distribution.
Importantly, these scans are performed on the same DXA machine but use different scan options and reporting protocols depending on what information is being assessed.
Although both use the same technology, they are designed for very different purposes.
Here’s what you need to know.
What is a Diagnostic Bone Density (BMD) Scan?
A bone mineral density (BMD) scan is a medical imaging test used to assess bone strength and fracture risk.
This type of scan is commonly requested by a doctor when there are concerns relating to:
Osteoporosis or osteopenia
Low-trauma fractures
Menopause-related bone loss
Long-term corticosteroid use
Low hormone levels
Medical conditions affecting bone health
Family history of osteoporosis
The scan focuses on key skeletal sites — most commonly the lumbar spine and hips — as these areas are highly predictive of fracture risk.
The report includes measurements such as:
T-scores (comparison to a healthy young adult population)
Z-scores (comparison to age-matched individuals)
Bone density measurements used to assess bone health
These results are interpreted alongside your medical history and risk factors to help assess conditions such as osteopenia and osteoporosis.
The Main Purpose
A BMD scan answers the question: “How healthy and strong are my bones?”
What is a Body Composition DEXA Scan?
A body composition DEXA scan uses the same underlying technology, but rather than diagnosing bone disease, it is designed to assess body composition.
Instead of focusing on fracture risk, a body composition scan measures:
Muscle mass (lean tissue)
Body fat percentage
Fat mass and lean mass distribution
Visceral adipose tissue (VAT) estimates
Left-to-right symmetry and regional body composition
Bone density average
This type of scan is commonly used by:
Athletes and active individuals
People pursuing fat loss or muscle gain goals
Individuals tracking progress over time
Health professionals monitoring body composition changes
People wanting more insight than scales or BMI can provide
Rather than simply telling you your body weight, a body composition scan helps explain what makes up your weight.
For example, two people may weigh exactly the same but have very different amounts of muscle and body fat.
The Main Purpose
A body composition scan answers the question:
“What is my body made up of?”
Aren’t They Both DEXA Scans?
Yes — and this is where much of the confusion happens.
A diagnostic BMD scan and a body composition DEXA scan are performed using the same DXA machine. However, they involve different scan modes selected by the technician, with each scan designed to answer different clinical questions.
Think of it like using the same smartphone camera in different modes — portrait mode and panoramic mode use the same device, but they are designed to capture different information.
When a diagnostic bone density scan is selected, the machine follows a validated protocol specifically designed to assess bone mineral density and fracture risk, focusing on key regions such as the lumbar spine and hips. This scan generates diagnostic T-scores and Z-scores used to assess conditions such as osteopenia and osteoporosis.
When a body composition scan is selected, the machine uses a different protocol designed to assess muscle mass, body fat, lean tissue and body composition distribution across the entire body.
While a body composition scan does provide a general snapshot of bone mineral content and density, it is not considered the diagnostic version of a bone density assessment. It does not replace a formal BMD scan for assessing osteoporosis risk or generating diagnostic bone health scores.
In simple terms:
A BMD scan asks: “How healthy and strong are my bones?”
A body composition DEXA scan asks: “What is my body made up of?”
The Bottom Line
Although both scans are performed on the same DEXA machine, they are used for different purposes.
A diagnostic bone density scan (BMD) is a medical imaging investigation used to assess bone health and fracture risk. Because of this, it generally requires a doctor’s referral and includes a radiologist report.
A body composition DEXA scan, on the other hand, is designed to assess muscle mass, body fat and body composition. These scans can be booked directly without a referral and interpreted by our dietitians to support nutrition, health and performance goals.
