DXA Body Sites
DXA scans routinely evaluate three primary skeletal sites: the hip (total hip and femoral neck), the lumbar spine (L1-L4), and the forearm (specifically the one-third/33% radius region). 1
Standard Measurement Sites
Hip
- Total hip and femoral neck are standard measurement sites
- The femoral neck is designated as the reference site for epidemiological studies
- Non-dominant hip is typically measured
- If one hip is not evaluable (e.g., hip arthroplasty), the contralateral side should be assessed 1
Lumbar Spine
- L1-L4 region is the standard measurement area
- Images are acquired posterior-to-anterior (PA), though often called AP scans
- Vertebrae affected by structural changes (compression fractures, severe osteoarthritis, surgical implants) should be excluded from analysis 1
Forearm
- One-third (33%) radius is the standard forearm measurement site
- Non-dominant arm should be scanned
- Includes both radius and ulna measurements 1
When Forearm Scanning is Indicated
A forearm scan should be performed when:
- Lumbar spine and/or hip contain artifacts that limit interpretation (fractures, implants, degenerative changes)
- Patient exceeds the weight limit of the scanner table
- Patient cannot be positioned comfortably on the table
- Hyperparathyroidism is diagnosed (forearm scan should always be performed) 1
- Large discordance exists (>1 T-score unit) between lumbar and hip scans 1
Important Caveat for Forearm Measurements
In chronic arthritides such as rheumatoid arthritis, BMD should NOT be measured at the radius due to local juxta-articular bone loss that results in falsely lower BMD than other skeletal sites 1
Additional DXA Capabilities
Vertebral Fracture Assessment (VFA)
- VFA imaging typically captures T4 through L5 vertebrae
- Most vertebral fractures occur between T6 through L4
- The majority of VFs are found in this mid-thoracic to lumbar region 2
Whole Body Composition
- DXA can perform whole-body scans to determine bone and soft tissue composition
- Can assess subregions including arms, legs, and trunk 3
Diagnostic Application
The WHO diagnostic criteria apply to measurements at the lumbar spine, one-third radius, femoral neck, or total hip—a T-score ≤ -2.5 at any of these sites is consistent with osteoporosis. 1 Diagnostic classification is based on the lowest T-score at any of the recommended DXA regions.