What are the guidelines for ordering a Dual-Energy X-ray Absorptiometry (DEXA) scan to assess bone mineral density in patients at risk of osteoporosis?

DEXA Scan Guidelines for Osteoporosis Assessment

Dual-Energy X-ray Absorptiometry (DEXA) scanning of the lumbar spine and hip(s) is the primary recommended modality for osteoporosis screening in at-risk populations, with specific timing for initial and follow-up scans based on risk factors. 1

Who Should Receive DEXA Scans

General Population Screening

• Women ≥65 years of age
• Men ≥70 years of age
• Postmenopausal women <65 years with additional risk factors for fracture

High-Risk Individuals (Any Age)

1. Medical conditions affecting bone mineral density:

   • Chronic renal failure
   • Rheumatoid arthritis and inflammatory arthritides
   • Eating disorders (anorexia nervosa, bulimia)
   • Organ transplantation recipients
   • Prolonged immobilization
   • Malabsorption conditions (celiac disease, inflammatory bowel disease)
   • Vitamin D deficiency
   • Endocrine disorders (hyperparathyroidism, hyperthyroidism, Cushing syndrome)
   • Multiple myeloma
   • Post-gastric bypass surgery

2. Medication use:

   • Glucocorticoid therapy (≥5 mg prednisone equivalent daily for ≥3 months)
   • Anticonvulsants
   • Aromatase inhibitors
   • Androgen deprivation therapy
   • Chronic heparin therapy

3. Other risk factors:

   • Previous fragility fracture
   • Hypogonadal men >18 years
   • Family history of hip fracture
   • Low body mass index
   • Smoking
   • Excessive alcohol consumption

Recommended Testing Sites

Primary Testing:

• Lumbar spine and hip(s) - rated 9/9 (usually appropriate) 1
  • Most reliable for initial assessment and monitoring

Special Circumstances:

• Distal forearm - when hip/spine cannot be measured or interpreted 1

  • Specifically indicated in hyperparathyroidism
  • When patient exceeds weight limit for DEXA table

• Quantitative CT (QCT) - for patients with advanced degenerative changes of the spine (rated 8/9) 1

  • Provides volumetric BMD measurement
  • Avoids falsely elevated readings from degenerative changes

Follow-Up Recommendations

General Follow-Up Timing:

• Every 2 years for most patients with established low BMD 1
• Every 1-2 years after initiating therapy 1
• Every 1 year for patients at high risk for rapid bone loss (e.g., glucocorticoid therapy) 1
• Avoid intervals <1 year as they are not clinically useful 1

Special Populations:

• Primary Sclerosing Cholangitis (PSC): DEXA scan at diagnosis with follow-up according to standard guidelines 1
• Premenopausal women and men <50 years with risk factors: Follow-up every 1-2 years if high risk for accelerated bone loss, otherwise every 2 years 1

Vertebral Fracture Assessment (VFA)

VFA is recommended in conjunction with DEXA for patients with:

• T-scores less than -1.0 AND one or more of:
  • Women ≥70 years or men ≥80 years
  • Historical height loss >4 cm (>1.5 inches)
  • Self-reported but undocumented prior vertebral fracture
  • Glucocorticoid therapy ≥5 mg prednisone daily for ≥3 months 1

Important Technical Considerations

• Patients should be scanned on the same DEXA machine for follow-up assessments 1
• BMD values (not T-scores) should be compared between scans 1
• In cases of falsely elevated spine readings due to degenerative changes, up to 2 vertebral levels may be excluded 1
• If more than 2 levels need exclusion, scan the second hip or distal one-third radius 1

Interpretation and Treatment Thresholds

• Normal: T-score ≥ -1.0
• Osteopenia: T-score between -1.0 and -2.5
• Osteoporosis: T-score ≤ -2.5 or fragility fracture regardless of T-score

For glucocorticoid-induced osteoporosis, consider treatment at higher BMD values (T-score < -1.5) 2

Cost-Effectiveness Considerations

Prescreening questionnaires identifying risk factors can help optimize DEXA utilization, potentially reducing diagnostic costs per osteoporotic patient detected by 9-23% 3. This approach is particularly valuable for excluding low-risk subjects rather than selecting osteoporotic patients.

Common Pitfalls to Avoid

1. Degenerative changes: Spine BMD may be falsely elevated in patients with spondylosis or facet arthritis (affects >81% of falsely elevated measurements) 1

2. Inconsistent follow-up machines: Cross-calibration is required if different machines must be used 1

3. Improper timing: Scanning too frequently (<1 year) provides no clinical benefit and increases costs 1

4. Missing vertebral fractures: Up to 23% of patients with normal BMD may have vertebral fractures, highlighting the importance of VFA in appropriate patients 1

5. Underutilization: Only 6.7% of patients undergo DEXA within 6 months after fragility fracture, and only 8% on long-term glucocorticoid therapy receive appropriate follow-up 1