Bone Density (DEXA) Scan
Bone Density (DEXA) Scan in Pediatrics
Key Points
- Dual-energy X-ray absorptiometry (DEXA) is the gold standard for measuring bone mineral density (BMD) in children
- Results must be adjusted for age, sex, height, and pubertal status
- Z-scores, not T-scores, are used in pediatric populations
- BMD values below -2.0 Z-score indicate low bone mass for chronologic age
Overview
DEXA scanning uses low-dose X-ray beams to measure bone mineral content (BMC) and bone mineral density (BMD). In pediatrics, it's particularly valuable due to its:
- Low radiation exposure (0.001-0.006 mSv)
- High precision (error rate < 1%)
- Short scan time (5-10 minutes)
- Ability to measure specific skeletal sites
Primary Clinical Indications
- Chronic inflammatory conditions
- Inflammatory bowel disease
- Juvenile idiopathic arthritis
- Cystic fibrosis
- Endocrine disorders
- Growth hormone deficiency
- Hypogonadism
- Type 1 diabetes
- Immobilization
- Cerebral palsy
- Muscular dystrophy
- Spinal cord injuries
- Medications affecting bone metabolism
- Long-term glucocorticoids
- Anticonvulsants
- Chemotherapy
Scan Protocol
- Standard measurement sites:
- Lumbar spine (L1-L4) - Primary site for children
- Total body less head (TBLH)
- Proximal femur (in older adolescents)
- Patient positioning:
- Supine position
- Proper alignment using laser guides
- Use of positioning devices for consistency
Quality Assurance
- Daily phantom calibration
- Regular technologist training
- Motion artifact monitoring
- Regular maintenance and calibration
Result Analysis
- Z-score interpretation:
- ≤ -2.0: Low bone mass for chronologic age
- -1.9 to -1.0: Below average for age
- -0.9 to +0.9: Average for age
- ≥ +1.0: Above average for age
- Essential adjustments:
- Height-for-age Z-score
- Bone age assessment
- Pubertal staging
- Body composition
Clinical Correlation
- Assessment of fracture risk
- Growth velocity monitoring
- Treatment response evaluation
- Longitudinal tracking
Technical Limitations
- Two-dimensional nature of measurements
- Cannot distinguish cortical from trabecular bone
- Motion artifacts in young children
- Size-related artifacts in small children
Clinical Considerations
- Growth and maturation effects
- Need for sedation in young children
- Cost and availability
- Radiation exposure (though minimal)
