Is a DEXA (Dual-Energy X-ray Absorptiometry) scan result necessary to start bisphosphonate therapy?

DEXA Scan Is Not Absolutely Required to Start Bisphosphonate Therapy

In most clinical scenarios, you can initiate bisphosphonate therapy without a DEXA scan if the patient has clear clinical indications, particularly in patients over 65 years with risk factors or those with documented fragility fractures. However, DEXA scanning provides valuable baseline information for monitoring treatment response and is strongly recommended when feasible.

When You Can Start Bisphosphonates WITHOUT a DEXA Scan

Patients with Documented Fragility Fractures

• Any patient with a documented fragility fracture (vertebral, hip, or other) can be started on bisphosphonates immediately without DEXA confirmation, as the fracture itself is diagnostic of osteoporosis 1
• Vertebral fractures are considered diagnostic of osteoporosis even if spine BMD values would not be in the osteoporotic range 2

Older Adults with High Clinical Risk

• Patients aged 65 years and older with risk factors can be started on bisphosphonates without DEXA, since the vast majority will have a T-score of -1.5 or below 1
• This is particularly relevant for glucocorticoid-induced osteoporosis, where treatment should be considered at T-scores of <-1.5 rather than the standard -2.5 threshold 1

Glucocorticoid-Induced Osteoporosis

• Patients receiving systemic glucocorticoid therapy equivalent to ≥5 mg prednisone daily for ≥3 months should receive calcium and vitamin D for prophylaxis, and bisphosphonates can be initiated based on clinical judgment 2
• Fractures occur at higher BMD levels in glucocorticoid-induced osteoporosis compared to postmenopausal osteoporosis, making clinical assessment more important than DEXA results 1

When DEXA Scan IS Strongly Recommended Before Starting Therapy

Younger Patients (Under 65 Years)

• In younger individuals where BMD is likely to be higher, DEXA is useful in determining if bone protective treatment is needed immediately or if it could be delayed until the T-score falls below -1.5 1
• This prevents unnecessary treatment in patients who may not yet meet treatment thresholds

Patients Without Clear Fracture History

• DEXA provides objective confirmation of osteoporosis (T-score ≤ -2.5) or osteopenia (T-score between -1.0 and -2.5) to guide treatment decisions 2
• The diagnosis of osteoporosis in adults is best made from a T-score of less than -2.5 on radiographic bone densitometry 2

Establishing Baseline for Monitoring

• Although not absolutely necessary to initiate therapy, having a baseline DEXA scan is useful to assess treatment response and guide duration of therapy 1
• Patients receiving bisphosphonate therapy should have repeat DEXA every 1-2 years to monitor response 3

Clinical Algorithm for Decision-Making

Step 1: Assess for Immediate Treatment Indications (No DEXA Required)

• Documented fragility fracture? → Start bisphosphonates immediately
• Age ≥65 with risk factors? → Start bisphosphonates immediately
• Glucocorticoid therapy ≥3 months? → Start bisphosphonates immediately

Step 2: If No Immediate Indication, Consider DEXA

• Age <65 without fracture → Obtain DEXA before treatment decision
• Uncertain clinical risk → Obtain DEXA and calculate FRAX score
• Need baseline for monitoring → Obtain DEXA before or shortly after starting therapy

Step 3: Post-Treatment Monitoring

• Repeat DEXA every 1-2 years for patients on bisphosphonates 3
• Use same DXA machine and compare BMD values (not T-scores) between scans 2, 4

Important Clinical Pitfalls to Avoid

Don't Delay Treatment Waiting for DEXA in High-Risk Patients

• The most common error is delaying necessary treatment in elderly patients or those with fractures while waiting for DEXA scheduling 1
• In patients over 65 with clinical risk factors, the probability of having osteoporosis is high enough to justify empiric treatment 1

Don't Rely Solely on Bone Scans for Treatment Decisions

• Starting bisphosphonates in women with only an abnormal bone scan but without evidence of bone destruction on plain radiographs is not recommended 2
• Plain radiographic evidence of bone destruction or documented fractures are more reliable indicators 2

Consider Secondary Causes Before Assuming Primary Osteoporosis

• In younger patients or those with unexpectedly low BMD, evaluate for secondary causes such as hyperparathyroidism, malabsorption, vitamin D deficiency, or other metabolic bone diseases 2
• Serum vitamin D3 levels <20 ng/mL predict increased risk of adverse events and should be corrected 2