How should I order a dual‑energy X‑ray absorptiometry (DEXA) scan for bone density assessment?

How to Order a DEXA Scan for Bone Density Assessment

Order a DEXA scan to measure bone mineral density (BMD) at the lumbar spine, total hip, and femoral neck, with the one-third radius added if indicated (e.g., hyperparathyroidism, inability to measure spine/hip). 1

Who Should Get DEXA Screening

Routine Screening (No Additional Risk Factors Required)

• All women ≥65 years
• All men ≥70 years

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Younger Adults Requiring Screening (Age ≥50 but below routine screening age)

Order DEXA if ANY of the following apply:

• Previous fragility fracture (low-trauma fracture of hip, spine, forearm, humerus, pelvis)
• Chronic glucocorticoid use (≥5 mg prednisone equivalent daily for ≥3 months)
• Diseases associated with bone loss (hyperparathyroidism, rheumatoid arthritis, chronic kidney disease, malabsorption syndromes)
• Medications causing bone loss (aromatase inhibitors, androgen deprivation therapy, anticonvulsants)
• Anyone being considered for osteoporosis treatment
• Anyone where evidence of bone loss would change management

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For postmenopausal women <65 years, the USPSTF recommends a 2-step approach: first assess fracture risk using a clinical tool (like FRAX), then order DEXA if elevated risk is identified. 2

Younger Adults (<50 years, Premenopausal Women)

Order DEXA only with:

• Prior fragility fracture
• Specific diseases causing secondary osteoporosis
• Medications known to cause significant bone loss
• Conditions requiring treatment decisions based on BMD

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What to Order Specifically

Standard Protocol

Request "DEXA scan of lumbar spine, total hip, and femoral neck" - this is the standard three-site assessment. 1

Additional Sites When Indicated

Add one-third radius (33% radius) if:

• Hyperparathyroidism
• Severe obesity preventing spine/hip measurement
• Spine/hip cannot be measured or interpreted due to hardware, severe degenerative changes, or previous fracture

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Special Populations Requiring Non-Standard Sites

• Spinal cord injury patients: Order total hip, proximal tibia, and distal femur (requires specialized DXA machines and referral to specialized centers) 1

Ordering Vertebral Fracture Assessment (VFA)

Consider adding VFA to the DEXA order if the patient meets ANY of these criteria:

• Women ≥70 years OR men ≥80 years with T-score ≤-1.0
• Historical height loss >4 cm (>1.5 inches)
• Self-reported but undocumented prior vertebral fracture
• Chronic glucocorticoid therapy (≥5 mg prednisone equivalent daily for ≥3 months)
• T-score ≤-2.5 at spine or hip
• Acute onset back pain with osteoporosis risk factors

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VFA can detect prevalent vertebral fractures that may not be clinically apparent but significantly impact treatment decisions.

Critical Ordering Details

For Baseline Scans

Simply order: "DEXA bone density scan with BMD measurement of lumbar spine, total hip, and femoral neck [+/- one-third radius if indicated] [+/- VFA if indicated]"

For Follow-Up Scans

Specify: "Repeat DEXA at same facility as [date of prior scan], using same machine and protocol for comparison"

This is crucial because BMD changes are only meaningful when compared using the same equipment and technique. The least significant change (LSC) that indicates real bone loss is typically 2.8-5.6%, depending on the facility's precision. 1

Follow-Up Interval Recommendations

Typical intervals are 1-5 years depending on clinical circumstances:

• Patients on treatment: 1-2 years after starting or changing therapy
• High-risk untreated patients: 1-2 years
• Lower-risk patients: 2-5 years
• Stable treated patients: 2-3 years

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Common Pitfalls to Avoid

1. Don't order DEXA in men <70 or women <65 without documented risk factors - this leads to overdiagnosis and unnecessary treatment 2

2. Don't use peripheral DXA devices (heel, finger) for diagnosis - only central DXA measuring spine and hip is acceptable for diagnosis and treatment decisions 2

3. Don't order too-frequent repeat scans - changes smaller than the LSC (typically <3-6%) are measurement noise, not real change 1

4. Don't forget to specify VFA when indicated - up to 25% of patients have unrecognized vertebral fractures that would change management 1

5. For transgender patients: Specify whether to use birth sex or gender identity reference data based on hormone therapy status and duration 1