From the Guidelines
Dual-Energy X-ray Absorptiometry (DXA) scans for measuring bone fragility primarily come in two main types: central DXA and peripheral DXA, with central DXA being the gold standard for osteoporosis diagnosis and fracture risk assessment, as it measures bone mineral density (BMD) at the hip and lumbar spine, which are the most clinically relevant sites 1.
Types of DXA Scans
- Central DXA: This is the most commonly used method and measures BMD at the hip and lumbar spine, providing accurate assessments of fracture risk and osteoporosis diagnosis 1.
- Peripheral DXA: This measures BMD at appendicular sites such as the forearm, finger, heel, or wrist, offering a more portable and less expensive alternative, though it's less accurate for diagnosis and monitoring than central DXA.
DXA Scan Procedure
DXA technology works by using two X-ray beams with different energy levels to distinguish between bone and soft tissue, providing precise measurements of bone mineral content 1.
Interpretation of Results
Results are typically reported as T-scores (comparison to young adult peak bone mass) and Z-scores (comparison to age-matched controls), with T-scores below -2.5 indicating osteoporosis 1.
Recommendations for Use
For optimal assessment, central DXA of the hip and spine is recommended for osteoporosis screening or initial imaging of clinically suspected low BMD, as it is a clinically proven method of measuring BMD in these areas 1.
Additional Considerations
In addition to DXA, other techniques like Quantitative Computed Tomography (QCT) can provide volumetric BMD (vBMD) and assess both trabecular and cortical bone compartments, but its application and interpretation differ from DXA, particularly in monitoring bone loss over time 1.
From the Research
Types of DXA Scans
- Central DXA: This is the most commonly used method of measuring bone mineral density in clinical practice, and it is rapid and reliable 2.
- Peripheral DXA (pDXA): This type of scan is used to measure bone density at the calcaneus (heel bone) and can be used to diagnose low bone mass in women over 65 years of age 3.
- Whole-body DXA scans: These scans can be used to determine the bone and soft tissue composition of the whole body and subregions such as arms, legs, and trunk 4.
Measurement Sites
- Spine: DXA scans can be used to measure bone mineral density at the spine, which is an important site for assessing osteoporosis risk 5, 3.
- Hip: DXA scans can also be used to measure bone mineral density at the hip, which is another important site for assessing osteoporosis risk 5, 3.
- Calcaneus: pDXA scans can be used to measure bone density at the calcaneus, which can be used to diagnose low bone mass in women over 65 years of age 3.
- Forearm: Some DXA instruments can also measure bone mineral density at the forearm 4.
Clinical Applications
- Osteoporosis diagnosis and treatment: DXA scans can be used to diagnose osteoporosis and monitor the effects of treatment 5, 6.
- Fracture risk assessment: DXA scans can be used to assess an individual's risk of fracture, which can help guide treatment decisions 6.
- Body composition analysis: DXA scans can also be used to measure body composition, including fat and fat-free mass 4.