What are the recommendations for Dual-Energy X-ray Absorptiometry (DEXA) scans in patients on Glucagon-Like Peptide-1 (GLP-1) analogs, such as exenatide (Byetta) or liraglutide (Victoza)?

DEXA Scan Recommendations for Patients on GLP-1 Receptor Agonists

Primary Recommendation

Patients on GLP-1 receptor agonists should undergo baseline DEXA scanning of the lumbar spine and bilateral hips before initiating therapy if they have any additional risk factors for osteoporosis, and follow-up DEXA scanning every 2 years during treatment to monitor bone mineral density, particularly if significant weight loss occurs. 1

Risk Assessment and Baseline Screening

High-Risk Patients Requiring Baseline DEXA Before GLP-1 Initiation

• Postmenopausal women of any age starting GLP-1 therapy should undergo baseline DEXA scanning 1
• Men ≥70 years initiating GLP-1 agonists require baseline screening 1
• Any patient on concurrent glucocorticoid therapy (≥5 mg prednisone equivalent daily for ≥3 months) must have DEXA scanning regardless of age 1
• Patients with body weight <127 lb (58 kg) before starting GLP-1 therapy 1
• History of parental hip fracture 1
• Prior fragility fracture 1
• Endocrine disorders affecting bone metabolism (hypogonadism, hyperthyroidism, hyperparathyroidism) 1
• Chronic kidney disease Stage 3-5 patients starting GLP-1 therapy 2
• Inflammatory bowel disease (particularly Crohn's disease) patients on GLP-1 agonists 3
• Post-bariatric surgery patients now being treated with GLP-1 agonists 4

Standard Screening Protocol

• DEXA of lumbar spine (L1-L4) and bilateral hips is the gold standard imaging modality 1, 5
• For patients with advanced degenerative spine changes, scoliosis, or ankylosing spondylitis, consider DEXA of the distal forearm as an alternative site, as lumbar spine measurements can be falsely elevated by osteophytes in >81% of cases 1
• Obtain post-dialysis weight for hemodialysis patients or post-drain weight for peritoneal dialysis patients when performing DEXA 2

Monitoring Schedule During GLP-1 Therapy

Frequency of Follow-Up DEXA Scans

• Every 1-2 years for patients on concurrent glucocorticoid therapy while taking GLP-1 agonists 1
• Every 2 years for all patients on GLP-1 therapy who have baseline osteopenia (T-score -1.0 to -2.5) or osteoporosis (T-score ≤-2.5) 1
• Every 2 years for patients experiencing significant weight loss (>10% body weight) on GLP-1 therapy 4
• Every 2-3 years for patients with normal baseline BMD and no additional risk factors 2

Special Monitoring Situations

• Patients with inflammatory bowel disease on GLP-1 agonists require DEXA if they have persistently active disease or repeated corticosteroid exposure 3
• Chronic kidney disease patients eligible for transplantation should have DEXA performed before transplant 2
• Post-bariatric surgery patients now on GLP-1 therapy require DEXA every 2 years 4

Interpretation of Results

Score Reporting Standards

• Use T-scores for postmenopausal women and men ≥50 years on GLP-1 therapy 1
• Use Z-scores (not T-scores) for premenopausal women and men <50 years; Z-scores ≤-2.0 are considered below expected age range 1
• T-score ≤-1.5 in patients with primary biliary cholangitis or primary sclerosing cholangitis indicates high risk for hip and vertebral fractures and warrants specific therapy 2

Critical Pitfalls to Avoid

• Do not rely solely on lumbar spine DEXA in patients with degenerative changes, as osteophytes can falsely elevate BMD measurements 1
• Do not delay screening in young adults with hypogonadism or other high-risk conditions until standard age thresholds 1
• Do not use actual body weight for very obese or underweight patients; use adjusted edema-free body weight for calculations 2

Bone Protection During GLP-1 Therapy

Nutritional Supplementation

• All patients on GLP-1 agonists should receive:
  • Ages 19-50: 1,000 mg calcium + 600 IU vitamin D daily 1
  • Ages 51-70: 1,200 mg calcium + 600 IU vitamin D daily 1
  • Ages 71+: 1,200 mg calcium + 800 IU vitamin D daily 1
• Patients with inflammatory bowel disease on GLP-1 therapy require 800-1,000 mg/day calcium and 800 IU/day vitamin D 3

Lifestyle Modifications

• Weight-bearing exercise should be encouraged during GLP-1 therapy to minimize bone loss 1, 4
• Smoking cessation is essential 1
• Alcohol moderation is recommended 1

Evidence Regarding GLP-1 Effects on Bone

Protective Effects Observed

• Exenatide treatment for 24 weeks in postmenopausal women with T2DM showed decreased RANK and RANKL levels (bone resorption markers) and increased osteoprotegerin, suggesting early antiresorptive effects, with no decrease in BMD despite weight loss 6
• Combination of exercise plus liraglutide preserved bone health at the hip and lumbar spine despite 16.88 kg weight loss over 52 weeks 7
• Exenatide monotherapy increased total hip BMD after 52 weeks of treatment 8

Concerning Findings

• Liraglutide alone (without exercise) reduced BMD at the hip and spine more than exercise alone despite similar weight loss 7
• Dulaglutide showed decreased femoral neck BMD after 52 weeks, though the magnitude was less than placebo 8

Clinical Interpretation

The evidence suggests that GLP-1 receptor agonists combined with weight-bearing exercise provide the best bone protection during weight loss 7. When GLP-1 therapy is used without structured exercise, closer monitoring with DEXA is warranted, particularly at the hip and femoral neck 7, 8.

Management of Abnormal Results

If Osteopenia Detected (T-score -1.0 to -2.5)

• Continue calcium and vitamin D supplementation at age-appropriate doses 1
• Intensify weight-bearing exercise program 1, 4
• Repeat DEXA in 2 years 1
• Consider bisphosphonate therapy if T-score approaches -2.5 or if additional risk factors present 3

If Osteoporosis Detected (T-score ≤-2.5)

• Initiate bisphosphonate therapy (postmenopausal women and men with osteoporosis) 3
• Continue GLP-1 therapy with enhanced bone protection measures 6, 7
• Repeat DEXA every 1-2 years to monitor treatment response 1
• Ensure adequate calcium (1,200 mg/day) and vitamin D (800 IU/day minimum) 1