Role of DEXA Scan in Diagnosing and Managing Osteoporosis
Dual-Energy X-ray Absorptiometry (DEXA) is the gold standard imaging modality for diagnosing osteoporosis, predicting fracture risk, and monitoring treatment effectiveness, serving as the primary tool for bone mineral density (BMD) assessment in clinical practice. 1, 2
Screening Recommendations
Who Should Be Screened
- All women aged 65 years and older and men aged 70 years and older should undergo routine DEXA screening regardless of risk factors 3, 1
- Women younger than 65 years and men younger than 70 years with additional risk factors should be screened, including: 1
- Individuals with bone mass osteopenia or fragility fractures on imaging studies (radiographs, CT, MRI) 1
- Individuals aged 50 years and older who develop a wrist, hip, spine, or proximal humerus fracture with minimal trauma 1
- Individuals of any age who develop one or more insufficiency fractures 1
High-Risk Groups Requiring Earlier Screening
- Adults with previous fragility fractures 3
- Individuals on long-term glucocorticoid therapy 3
- Individuals with medical conditions associated with bone loss (hyperparathyroidism, hypogonadism) 3
- Individuals taking medications associated with bone loss 3
Diagnostic Criteria and Interpretation
T-scores and Diagnostic Categories
- Normal BMD: T-score greater than -1.0 1
- Osteopenia (low bone mass): T-score between -1.0 and -2.4 1
- Osteoporosis: T-score equal to or less than -2.5 1
- Z-scores (comparison to age-matched controls) are used to detect secondary causes of osteoporosis 1
Measurement Sites
- Standard DEXA examination includes two sites: lumbar spine and hip 1
- In the spine, frontal projection measures up to 4 vertebral bodies from L1 to L4 1
- In the hip, frontal projection measures femoral neck and total hip 1
- Distal one-third radius of the nondominant arm may be used as a third site when:
Limitations and Considerations
- DEXA may overestimate BMD in taller individuals and underestimate BMD in petite individuals 1
- Caution is required when interpreting BMD changes with significant weight gain or loss 1
- Advanced degenerative changes in the spine can falsely elevate BMD measurements 1
- In cases of fracture, facet joint osteoarthritis, or spondylosis affecting the spine, up to 2 vertebral levels may be excluded from analysis 1
Fracture Risk Assessment
FRAX Tool
- For patients with low bone mass (T-scores between -1.0 and -2.4), the FRAX tool should be used to calculate 10-year fracture risk 1
- FRAX factors include hip BMD, age, gender, height, weight, family history of hip fracture, smoking, steroid use >3 months, rheumatoid arthritis, and alcohol use 1
- The National Osteoporosis Foundation recommends treatment in patients with:
Vertebral Fracture Assessment (VFA)
- VFA can further predict fracture risk, particularly in patients with osteopenia 1
- Recommended for individuals with T-score <-1.0 and one or more of the following: 3
- Women aged ≥70 years or men aged ≥80 years
- Historical height loss >4 cm
- Self-reported but undocumented prior vertebral fracture
- Oral glucocorticoid therapy equivalent to ≥5 mg prednisone daily for ≥3 months
Monitoring Treatment
Follow-up Intervals
- Individuals being monitored to assess the effectiveness of osteoporosis drug therapy 1
- For individuals with normal bone density or mild osteopenia: repeat DEXA in 2-3 years 3
- For individuals with osteoporosis or on treatment: repeat DEXA in 1-2 years 3, 4
Treatment Response Assessment
- Serial DXA scans are used to track expected gains in BMD with therapy 4
- With some drug therapies, BMD targets can be reached where further improvements in BMD are not associated with further reductions in fracture risk 4
- For patients who do not respond to therapy with improved BMD or who have an incident fragility fracture while on therapy, secondary causes of osteoporosis or non-compliance should be considered 4
Alternative Modalities
Quantitative CT (QCT)
- Provides volumetric BMD, in contrast to the areal BMD of DEXA 1
- Useful in patients with advanced degenerative changes in the spine 1
- May detect osteoporosis in patients classified as normal by DEXA, particularly those with aortic calcifications 1
- Recommended threshold ranges: normal (BMD > 120 mg/cm³), osteopenia (120 ≥ BMD ≥ 80 mg/cm³), and osteoporosis (BMD < 80 mg/cm³) 1
Clinical Impact
- DEXA scanning is critical in substantially reducing osteoporosis-associated morbidity and mortality 1
- Approximately half of women and nearly one-third of men over 50 years of age will sustain an osteoporotic fracture 1
- These fractures are associated with decreased quality of life, diminished physical function, and reduced independence 1, 5
- Most individuals who sustain fragility fractures have T-scores above the -2.5 cutoff, posing a challenge to clinicians 5