What is the recommended test for diagnosing osteoporosis?

Recommended Test for Diagnosing Osteoporosis

Dual-energy X-ray absorptiometry (DXA) of the lumbar spine and bilateral hips is the gold standard diagnostic test for osteoporosis. 1

Primary Diagnostic Modality

DXA scanning is the accepted reference standard for measuring bone mineral density (BMD) and diagnosing osteoporosis in both men and women. 1, 2 The test should measure:

• Lumbar spine (L1-L4) 1, 3
• Bilateral hips (femoral neck and total hip) 1, 3
• One-third (33%) radius (in specific circumstances) 1

The diagnosis is based on the lowest T-score at any of these recommended sites. 1

Diagnostic Criteria Using DXA

For Postmenopausal Women and Men ≥50 Years

Use T-scores for interpretation: 1, 3

• T-score ≤ -2.5 = Osteoporosis 1
• T-score between -2.5 and -1.0 = Osteopenia/low bone mass 1
• T-score ≥ -1.0 = Normal BMD 1

For Premenopausal Women, Men <50 Years, and Children

Use Z-scores (not T-scores) for interpretation: 1, 3, 4

• Z-score ≤ -2.0 = BMD below expected range for age 1, 3
• The International Osteoporosis Foundation (IOF) allows T-score ≤ -2.5 to diagnose osteoporosis in younger adults only in the presence of skeletal fragility 1

Alternative Diagnostic Approach

A prior low-trauma major osteoporotic fracture establishes the diagnosis of osteoporosis even with normal BMD. 1 Recent consensus from EANM, ASBMR, and CSEM supports presuming osteoporosis when a fragility fracture has occurred at the hip, spine, forearm, humerus, pelvis, ribs, or tibia (excluding ankle). 1

When to Consider Alternative Testing Sites

Forearm DXA (Distal One-Third Radius)

Consider when: 1, 3

• Advanced degenerative spine changes make lumbar spine unreliable 3, 5
• Scoliosis or ankylosing spondylitis present 3
• Severe obesity (BMI >35) limits hip/spine imaging 5

Critical caveat: Forearm measurements are not the most relevant site for fracture risk assessment and should be used cautiously. 1

Quantitative CT (qCT)

The American College of Radiology recommends qCT as the primary modality when: 5

• Severe degenerative spine disease is present 5
• Extremes in height or obesity (BMI >35) 5
• Monitoring treatments affecting primarily trabecular bone 5

Why this matters: DXA can falsely elevate BMD measurements by 81% in patients with osteophytes and degenerative facet disease, leading to underdiagnosis precisely in elderly patients who need treatment most. 5 One study found 44% of fracture patients were classified as osteoporotic by DXA versus 81% by quantitative CT. 5

Tests That Are NOT Recommended as Substitutes

Quantitative Ultrasonography (QUS)

While calcaneal ultrasonography predicts fractures in men, it cannot replace DXA for initiating therapy because treatment trials have not established effectiveness of therapy for osteoporosis diagnosed by ultrasonography rather than DXA. 1 Available evidence indicates QUS is neither sufficiently sensitive nor specific at predicting DXA-determined bone mass to substitute for DXA. 1

Peripheral BMD Measurements

Results from peripheral DXA devices cannot be interpreted using WHO diagnostic criteria, and their use is premature until consensus establishes equivalent thresholds. 2

Common Pitfalls to Avoid

Do not rely solely on spine DXA in patients with degenerative changes. 3, 5 Osteophytes, facet joint arthritis, and vertebral sclerosis falsely elevate lumbar spine BMD, causing underdiagnosis in the exact population being screened. 5 Consider hip-only measurements or alternative modalities (qCT) in these patients. 5

Do not use T-scores in premenopausal women or men <50 years unless skeletal fragility is present. 1, 3 Use Z-scores instead to avoid misclassification. 1, 3

Ensure proper scan technique: Both initial and follow-up scans must use the same DXA system, software, scan mode, patient positioning, and anatomical side to enable accurate comparisons. 1 Changes in BMD should be evaluated using absolute values (g/cm²), not T-scores or Z-scores. 1

Exclude vertebrae with structural abnormalities (compression fractures, surgical hardware, vascular calcifications) from analysis by carefully reviewing scan images, not just the numerical report. 5