In a patient on bisphosphonate therapy, should a Dual-energy X-ray absorptiometry (DEXA) scan be performed to monitor bone mineral density?

Yes, DEXA Scans Should Be Performed in Patients on Bisphosphonate Therapy

Patients on bisphosphonate therapy should undergo follow-up DEXA scans every 1-2 years initially until findings are stable, with the primary goals of monitoring treatment response, assessing for treatment failure, and guiding decisions about drug holidays or treatment changes. 1

Monitoring Framework

The most recent 2025 ISCD guidelines 2 and 2020 AACE/ACE guidelines 1 provide clear direction:

Initial Monitoring Phase

• Obtain baseline DEXA before starting bisphosphonates (lumbar spine, hip, and 1/3 radius if indicated)
• Repeat DEXA every 1-2 years until bone mineral density findings are stable 1
• After stability is achieved, continue monitoring at 1-2 year intervals or less frequently depending on clinical circumstances 1

Key Clinical Objectives for Follow-up DEXA

Follow-up BMD testing should be undertaken with clearly defined objectives 2:

1. Monitoring treatment response - Verify that therapy is working
2. Detecting treatment failure - Identify patients with continued bone loss despite therapy
3. Assessing compliance - Patients with declining BMD often have poor medication adherence (median MPR 0.54 vs 0.84 in stable patients) 3
4. Guiding drug holidays - Essential for determining when to stop or restart bisphosphonates
5. Evaluating new fractures or risk factors - Though testing should not delay secondary fracture prevention 2

Critical Decision Points Where DEXA Guides Management

Bisphosphonate Holiday Decisions

DEXA monitoring is essential for bisphosphonate holiday management 1:

• Oral bisphosphonates: After 5 years of treatment, consider a holiday if T-score >-2.5 and patient remains fracture-free. Continue up to 10 years if fracture risk remains high 1
• Zoledronate: Consider holiday after 3 years in high-risk patients or up to 6 years in very-high-risk patients 1
• Ending a holiday: Resume treatment if BMD decreases beyond the least significant change (LSC), fracture risk increases, or bone turnover markers rise 1

Repeat BMD testing is specifically required to monitor individuals prior to temporary cessation of bisphosphonate therapy and during the planned interruption period 2

Individualized Monitoring Intervals

The 2025 ISCD update emphasizes that intervals must be individualized based on 2:

• Patient's age and baseline BMD
• Type of pharmacological treatment
• Presence of factors associated with rapid bone loss (glucocorticoids, aromatase inhibitors, androgen deprivation therapy, malabsorption, bariatric surgery, surgical menopause)

Shorter intervals (potentially annual or more frequent) are indicated when rapid BMD changes are expected.

Important Caveats and Pitfalls

The "Too Little Too Late" Problem

Research shows that while DEXA monitoring can improve adherence in patients with declining BMD (MPR improved from 0.54 to 0.70), fracture rates remain elevated (22.4 vs 12.9 per 1000 person-years) compared to those with stable BMD 3. This highlights that adherence should be addressed at treatment initiation, not just when monitoring reveals problems.

Measurement Precision Matters

• Follow-up should ideally occur at the same facility with the same DEXA system 1
• Changes must exceed the least significant change (LSC) to be clinically meaningful 1
• The 1/3 radius site has a very large LSC, limiting its utility for monitoring 1

Early Monitoring May Be Misleading

One analysis suggests routine monitoring in the first 3 years may be unnecessary because between-person variation in bisphosphonate response is small compared to measurement variation 4. However, this conflicts with current guideline recommendations for 1-2 year monitoring.

Complementary Role of Bone Turnover Markers

Consider using bone turnover markers (BTMs) alongside DEXA 1:

• Significant BTM reductions with antiresorptive therapy are associated with fracture reduction
• BTMs can detect response as early as 3 months, before BMD changes become apparent 5
• Target: BTMs at or below the median for premenopausal women 1

When DEXA Results Should Prompt Action

If BMD changes are outside the expected range and adequate scan quality is confirmed, this should trigger 2:

• Reevaluation of the patient
• Reassessment of the treatment plan
• Consideration of referral to an osteoporosis specialist if recurrent fractures or continued bone loss occur despite therapy 1

Practical Implementation

Every DXA report should 2:

• State that follow-up is recommended as long as valid comparison is available
• Provide precise timing for next BMD if adequate clinical information is available
• Otherwise include a general recommendation about repeat testing

The bottom line: DEXA monitoring is not just recommended but essential for optimal bisphosphonate management, particularly for guiding drug holidays, detecting treatment failure, and individualizing therapy duration.