What are the recommendations for Dual-Energy X-ray Absorptiometry (DEXA) scans in patients at risk of osteoporosis, particularly older adults, postmenopausal women, or individuals with a history of fractures, thyroid disorders, rheumatoid arthritis, or prolonged steroid use?

DEXA Scan Recommendations for Osteoporosis Screening

Primary Screening Recommendations

All women aged 65 years or older should undergo routine DEXA screening regardless of risk factors, and all men aged 70 years or older should undergo routine DEXA screening. 1, 2

Age-Based Screening Thresholds

• Women ≥65 years: Universal screening recommended 1, 2
• Men ≥70 years: Universal screening recommended 1, 2
• Women <65 years: Screen only if postmenopausal with elevated risk factors 1, 2
• Men <70 years: Screen only with specific risk factors 2

High-Risk Populations Requiring Earlier Screening

DEXA screening should be performed immediately (regardless of age) in the following clinical scenarios:

Medical Conditions

• Previous fragility fracture (any low-trauma fracture of hip, spine, wrist, proximal humerus) 1, 2
• Chronic glucocorticoid therapy (≥5 mg prednisone daily for ≥3 months) 3, 1, 2
• Rheumatoid arthritis and other inflammatory arthritides 3
• Hyperparathyroidism or hyperthyroidism 3, 1, 2
• Hypogonadism (including premature menopause, oophorectomy before natural menopause) 3, 1, 4
• Chronic renal failure 3
• Eating disorders (anorexia nervosa, bulimia) 3
• Gastrointestinal malabsorption or malnutrition 3
• Organ transplantation 3
• Chronic alcoholism 3, 2
• Spinal cord injuries (as soon as medically stable) 1, 2

Medication-Induced Bone Loss

• Androgen deprivation therapy for prostate cancer 1, 2
• Aromatase inhibitor therapy 3
• Anticonvulsant drugs (long-term use) 3
• Chronic heparin therapy 3

Risk Assessment for Postmenopausal Women <65 Years

• Use FRAX calculator to determine 10-year fracture risk 3, 1
• Screen if 10-year major osteoporotic fracture risk ≥9.3% 1, 2
• Screen if 10-year hip fracture risk ≥3% 3, 1

Technical Specifications for DEXA Scanning

Anatomical Sites to Scan

Standard protocol includes measurement at three sites: 3

• Lumbar spine (L1-L4, excluding up to 2 vertebrae if falsely elevated by fracture or degenerative changes) 3
• Bilateral hips (total hip and femoral neck) 3
• Distal one-third radius of nondominant arm (third site when only one hip available, or primary site in hyperparathyroidism) 3

When to Use Alternative Sites

• Extensive spinal degenerative disease: Rely on hip measurements 3
• Severe obesity (BMI >35 kg/m²): Consider QCT as alternative 3
• Extreme body height: Consider QCT as alternative 3
• Hyperparathyroidism: Include distal radius (cortical-rich site preferentially affected) 3

Interpretation Guidelines

WHO Diagnostic Criteria (for postmenopausal women and men ≥50 years)

• Normal BMD: T-score ≥ -1.0 3
• Osteopenia (low bone mass): T-score between -1.0 and -2.5 3
• Osteoporosis: T-score ≤ -2.5 3
• Established osteoporosis: T-score ≤ -2.5 plus fragility fracture 3

Critical Interpretation Rules

• Fragility fracture supersedes DEXA measurement: Patients with osteopenic T-scores who have fragility fractures should be diagnosed with osteoporosis 3
• Use T-scores for all postmenopausal women and men ≥50 years 3, 4
• Use Z-scores for premenopausal women and men <50 years (diagnosis cannot be made on BMD alone in this population) 3
• Z-scores <-2.0 warrant investigation for secondary causes of osteoporosis 3

Follow-Up Scanning Intervals

Based on Initial Results and Risk Profile

• Normal BMD or mild osteopenia (T-score >-2.0): Repeat in 2-3 years 1, 2
• Moderate osteopenia (T-score -1.5 to -2.0): Repeat in 2 years 1
• Osteoporosis or on treatment: Repeat in 1-2 years to monitor treatment effectiveness 3, 1, 2
• High-risk for accelerated bone loss (glucocorticoid therapy, spinal cord injury): Repeat in 1-2 years 3, 1, 2

Evidence-Based Rationale for Intervals

• Minimum 2-year interval required to reliably measure BMD change due to testing precision limitations 1
• For 65-year-old women with normal baseline BMD, transition to osteoporosis takes approximately 17 years, supporting extended intervals 1
• For women with T-score -1.5 to -1.99, transition occurs in approximately 5 years 1
• Intervals <1 year are never recommended under any circumstances 1

Treatment Thresholds

Pharmacologic Treatment Recommended When:

• T-score ≤ -2.5 at any site (spine, hip, femoral neck) 3
• T-score between -1.0 and -2.5 PLUS FRAX-calculated 10-year hip fracture risk ≥3% 3
• T-score between -1.0 and -2.5 PLUS FRAX-calculated 10-year major osteoporotic fracture risk ≥20% 3
• Any fragility fracture regardless of T-score 3, 1
• Glucocorticoid-induced osteoporosis: T-score <-1.5 (lower threshold than postmenopausal osteoporosis) 5

Vertebral Fracture Assessment (VFA)

VFA should be performed during the same DEXA session in patients with: 1

• T-score <-1.0 AND any of the following:
  • Women ≥70 years or men ≥80 years 1
  • Historical height loss >4 cm 1
  • Self-reported but undocumented prior vertebral fracture 1
  • Glucocorticoid therapy ≥5 mg prednisone daily for ≥3 months 1

Special Population Considerations

Premenopausal Women and Men <50 Years

• Cannot diagnose osteoporosis by BMD alone in this population 3
• Use Z-scores (not T-scores) for interpretation 3
• Z-score <-2.0 indicates "below expected range for age" and warrants evaluation for secondary causes 3
• DEXA indicated only with specific risk factors (see High-Risk Populations section) 3

Transgender Individuals

• Calculate Z-scores using reference data conforming to gender identity 1, 2
• Post-pubertal transgender youth on GnRH agonists without sex steroid therapy are at risk for decreasing bone density 1

Patients with Chronic Alcoholism

• Immediate DEXA indicated regardless of age due to multiple mechanisms of bone loss 2
• Comprehensive metabolic workup required: calcium, phosphate, alkaline phosphatase, 25-hydroxyvitamin D, liver function tests, consider PTH 2
• Do not delay screening until age 65 2

Common Pitfalls and How to Avoid Them

Interpretation Errors

• Falsely elevated lumbar spine BMD: Degenerative changes, facet joint osteoarthritis, spondylosis, or vertebral fractures can artificially increase spine BMD 3, 4
  • Solution: Exclude up to 2 affected vertebrae; if >2 vertebrae affected, rely on hip measurements 3
• Using T-scores in premenopausal women or men <50: This leads to overdiagnosis 3
  • Solution: Use Z-scores exclusively in this population 3
• Assuming obesity protects against osteoporosis: While higher body weight is generally protective, it does not eliminate risk when other major risk factors are present 2
  • Solution: Screen obese patients with chronic alcoholism, glucocorticoid use, or other high-risk conditions 2

Screening Interval Errors

• Repeating DEXA too frequently (<2 years) in patients with normal BMD exposes patients to unnecessary radiation and cost without clinical benefit 1
  • Solution: Follow evidence-based intervals (minimum 2 years, often 2-3 years for normal BMD) 1
• Failing to recognize new risk factors that warrant earlier repeat testing 1
  • Solution: Assess for new conditions, medications, height loss >4 cm, or kyphosis at each clinical encounter 1

Underutilization

• Only 6.7% of patients undergo DEXA within 6 months after fragility fracture 3
• Only 8% of patients on long-term glucocorticoids have follow-up DEXA 3
• This underutilization leads to undertreatment in approximately 70% of high-risk patients 3
  • Solution: Implement systematic protocols for DEXA ordering in all fragility fracture patients and those starting long-term glucocorticoids 3

Machine Variability

• Different DXA machines may exhibit measurement variation unless cross-calibration has been performed 1
  • Solution: When possible, perform serial scans on the same machine; if changing machines, ensure cross-calibration 1