How do I interpret the results of a Dual-Energy X-ray Absorptiometry (DEXA) screening?

How to Read a DEXA Screening

Interpret DEXA scans systematically using the PARED approach (Positioning, Artifacts, Regions of Interest, Edge Detection, Demographics), focusing on T-scores for diagnosis in postmenopausal women and men over 50, where T-score ≤ -2.5 indicates osteoporosis, -1.0 to -2.5 indicates osteopenia, and ≥ -1.0 is normal. 1

Step 1: Verify Technical Quality Using PARED

Before interpreting any numbers, systematically evaluate the scan quality 1:

• P – Positioning: Check that the patient's body and limbs are aligned to midline with minimal rotation. Poor positioning invalidates the results 1
• A – Artifacts: Identify surgical hardware, vascular calcifications, undissolved calcium tablets, or contrast material that falsely elevate BMD 1
• R – Regions of Interest: Confirm the correct anatomical areas were scanned (lumbar spine L1-L4, total hip, femoral neck) and that ROIs are placed appropriately 1
• E – Edge Detection: Verify that bone edges are correctly identified by the software 1
• D – Demographics: Confirm patient age, sex, ethnicity, and risk factors are correctly entered, as these determine the reference database used 1

Step 2: Identify and Exclude Problematic Vertebrae

The lumbar spine is most frequently affected by artifacts that spuriously increase BMD values 1:

• Exclude any vertebra with facet joint osteoarthritis, osteophytes, or sclerosis—these falsely elevate readings in precisely the elderly patients you're screening 1
• Exclude vertebrae that differ by T-score ≥ 1.0 from adjacent vertebrae 1
• Exclude vertebrae with compression fractures, surgical hardware, or DISH (diffuse idiopathic skeletal hyperostosis) 1
• If degenerative changes are severe, consider requesting quantitative CT instead, as DEXA becomes unreliable 1, 2

Step 3: Read the T-Scores and BMD Values

Use T-scores (not Z-scores) for postmenopausal women and men over 50 3:

• Normal: T-score ≥ -1.0 3
• Osteopenia (Low Bone Mass): T-score between -1.0 and -2.5 3
• Osteoporosis: T-score ≤ -2.5 3
• Severe Osteoporosis: T-score ≤ -2.5 plus one or more fragility fractures 3

For premenopausal women, men under 50, and children, use Z-scores instead 3:

• Z-score ≤ -2.0 is considered "below the expected range for age" 3

The diagnosis is based on the lowest T-score from any measured site (lumbar spine, femoral neck, total hip, or 33% radius) 3

Step 4: Review the Complete Report Components

Every DEXA report must include 1:

• BMD in g/cm² for each site with corresponding T-scores 1
• Technical quality statement and any limitations (e.g., "Due to previous left hip replacement, scanning of right hip was performed") 1
• Comments on degenerative changes or artifacts that may affect interpretation 1
• Risk factors documented (smoking, family history, prior fractures, medications) 1
• FRAX score if calculated (10-year probability of hip fracture and major osteoporotic fracture) 1
• Diagnosis and treatment recommendations 1
• Follow-up timing (typically 2-3 years, or sooner if clinically indicated) 1

Step 5: Assess for Vertebral Fractures

Request Vertebral Fracture Assessment (VFA) if 3:

• T-score < -1.0 3
• Historical height loss ≥ 4 cm 3
• Prospective height loss ≥ 2 cm 3

An osteoporotic fracture supersedes any DEXA measurement and establishes the diagnosis regardless of T-score 3

Step 6: Calculate Fracture Risk

For patients with osteopenia, use FRAX to determine treatment need 3:

• Treatment recommended if 10-year hip fracture probability ≥ 3% 3
• Treatment recommended if 10-year major osteoporotic fracture probability ≥ 20% 3

Common Pitfalls to Avoid

Degenerative spine disease is the most critical pitfall 1, 2:

• Lumbar spine BMD can be falsely elevated by osteophytes, facet arthritis, and vertebral sclerosis—precisely the changes common in elderly patients being screened 1, 2
• One study found 44% of fracture patients were classified as osteoporotic by DEXA versus 81% by quantitative CT, demonstrating significant underdiagnosis 1
• For patients with severe spinal degeneration, scoliosis, or BMI > 35, request quantitative CT instead 2

Other artifacts that falsely elevate BMD 1:

• Aortic calcifications overlying vertebrae 1
• Surgical hardware or implantable devices 1
• Ankylosing spondylitis or DISH 1

Incorrect vertebral counting 1:

• Verify L1-L4 are correctly identified, as transitional vertebrae can cause misidentification 1

Monitoring Changes Over Time

When comparing serial scans 3, 4:

• Use absolute BMD values (g/cm²), not T-scores or Z-scores 3
• Ensure the patient returns to the same DXA machine 3, 4
• Calculate the Least Significant Change (LSC) for your facility—only changes exceeding LSC are clinically meaningful 3
• Typical follow-up interval is 2-3 years for stable patients 1, 4
• Shorten to 1-2 years for patients on glucocorticoids, androgen deprivation therapy, or other high-risk medications 4

CT Hounsfield units provide an alternative assessment 5:

• HU values > 160 indicate low osteoporosis risk 1
• HU values < 110 correlate significantly with osteoporosis 1
• CT shows positive correlation with DEXA BMD (r² = 0.58-0.65) and can provide opportunistic screening during routine abdominal imaging 5