DEXA Scan Screening Applications
DEXA (Dual-Energy X-ray Absorptiometry) primarily screens for osteoporosis by measuring bone mineral density (BMD) to identify individuals at risk of fractures due to low bone mass. 1
Primary Clinical Applications
Bone Mineral Density Assessment
- DEXA is the gold standard for diagnosing osteoporosis and monitoring treatment response 1
- Measures bone density at key skeletal sites:
- Posteroanterior spine (L1-L4)
- Total hip
- Femoral neck 2
- Results are reported as:
- T-scores: Comparison to young healthy adults (used for postmenopausal women and men ≥50)
- Z-scores: Comparison to age-matched peers (used for premenopausal women and men <50) 2
Screening Recommendations
- Women ≥65 years and men ≥70 years should receive routine screening 1, 2
- Younger individuals with risk factors should be screened earlier:
Special Populations
- Cancer patients receiving therapies affecting bone health:
- Aromatase inhibitors for breast cancer
- Androgen deprivation therapy for prostate cancer 1
- Patients on long-term glucocorticoid therapy 2
- HIV-infected postmenopausal women and men ≥50 years 2
Secondary Applications
Body Composition Analysis
- DEXA can assess regional and total body fat distribution 1
- Measures:
- Total body fat percentage
- Fat distribution patterns
- Lean tissue mass 1
Vertebral Fracture Assessment (VFA)
- Lateral spine imaging to detect existing vertebral fractures
- Indicated when height loss occurs (≥4 cm historical or ≥2 cm prospective) 1
- Enhances fracture risk assessment beyond BMD alone 2
Technical Considerations
Quality Assurance
- Precision and accuracy are critical for meaningful clinical data
- Daily phantom scans recommended for quality control 1
- Each facility should determine its precision error and calculate least significant change (LSC) 1
Interpretation Pitfalls
- Advanced degenerative changes in the spine may falsely elevate BMD values 2
- Patients should be scanned on the same DXA scanner for follow-up 2
- BMD values (not T-scores) should be compared between previous and current scans 2
Clinical Significance
DEXA scanning provides crucial information for fracture risk assessment and treatment decisions. The WHO diagnostic criteria define osteoporosis as a T-score ≤-2.5, osteopenia as T-score between -1.0 and -2.5, and normal as T-score ≥-1.0 1.
While alternative technologies like quantitative CT and ultrasound densitometry exist 3, 4, DEXA remains the preferred method due to its established predictive ability for fracture risk, proven effectiveness at targeting treatments, and ability to monitor response to therapy 5.