How do you interpret bone mineral density results in an older adult, likely a postmenopausal woman, with a history of osteoporosis or risk factors for osteoporosis?

Bone Mineral Density Interpretation

Diagnostic Criteria and T-Score Classification

Osteoporosis is diagnosed when the T-score is ≤-2.5 at the hip or lumbar spine, representing bone density 2.5 standard deviations or more below the mean for young healthy White women, which has become the reference standard for all racial and ethnic groups and both sexes. 1

• Osteopenia (low bone mass) is defined as a T-score between -1.0 and -2.5 2
• Normal bone density is defined as a T-score ≥-1.0 1
• T-scores compare the patient's BMD to a young adult reference population and are used for postmenopausal women and men ≥50 years 1

Age and Sex-Specific Interpretation Guidelines

Postmenopausal Women and Men ≥50 Years

Use T-scores for diagnosis in this population. 1

• The World Health Organization criteria apply to postmenopausal women and men ≥50 years 1
• A T-score ≤-2.5 confirms osteoporosis and warrants treatment consideration 1
• Diagnosis can also be made by the presence of a fragility fracture (low-trauma fracture from standing height or less), regardless of T-score 1, 3

Premenopausal Women and Men <50 Years

Use Z-scores (not T-scores) for this population, as WHO criteria do not apply. 1

• Z-scores compare BMD to age- and gender-matched controls 1
• Z-scores ≤-2.0 are defined as "below the expected range for age" 1
• Z-scores >-2.0 are "within the expected range for age" 1
• A diagnosis of osteoporosis cannot be made in men <50 years on the basis of BMD alone 1
• Z-scores should be population-specific where adequate reference data exist, using the patient's self-reported ethnicity 1

Site-Specific Measurement and Interpretation

DXA measurement should include the lumbar spine (L1-L4), total hip, and femoral neck as the gold standard for diagnosis. 1, 2

Lumbar Spine Considerations

• Exclude individual vertebral levels with spuriously elevated BMD due to degenerative changes, fractures, or facet arthropathy 1
• No more than two vertebral levels may be excluded from the L1-L4 calculation 1
• If more than two levels are affected by degenerative changes, exclude the entire spine and use the contralateral hip for diagnosis 1

Hip Measurement

• The hip is predominantly cortical bone and less sensitive to change than the cancellous-rich vertebrae 1
• If both hips are unsuitable (arthroplasty, advanced degeneration), the distal forearm can be substituted 1

Lowest T-Score Rule

Use the lowest T-score from any measured site (spine, total hip, or femoral neck) for diagnosis. 1

Racial and Ethnic Considerations in Interpretation

BMD alone does not fully capture fracture risk across different populations, as racial and ethnic groups show varying fracture incidence despite similar BMD values. 1

• African American women have higher average BMD than White women at any given age and lower fracture incidence 1, 2
• Asian women may have lower BMD than White women but paradoxically lower fracture risk 1, 2
• Hispanic populations show lower fracture incidence compared with White populations 1
• These differences are likely due to social and environmental factors or differences in clinical risks beyond BMD 1

Integration with Fracture Risk Assessment

For postmenopausal women <65 years with osteopenia (T-score -1.0 to -2.5), use FRAX or another clinical risk assessment tool to determine treatment thresholds. 1, 2

Treatment Thresholds Based on FRAX

• Initiate pharmacologic treatment when 10-year probability of major osteoporotic fracture is ≥20% 2
• Initiate pharmacologic treatment when 10-year probability of hip fracture is ≥3% 2
• Treat all patients with a history of low-trauma/fragility fracture regardless of FRAX score or BMD 2

Key Risk Factors Beyond BMD

• Advancing age is a stronger determinant of fracture risk than bone density alone 1
• Older adults have much higher fracture rates than younger adults with the same BMD due to declining bone quality and increased fall risk 1
• Additional risk factors include: low body weight (<127 lb or 57.6 kg), maternal hip fracture after age 50, current smoking, excess alcohol consumption, prolonged glucocorticoid use, and history of falls 1

Common Pitfalls in Interpretation

Degenerative Changes Causing False Elevation

Degenerative spondylosis and facet osteoarthritis can spuriously elevate lumbar spine BMD, leading to underdiagnosis of osteoporosis. 1

• Always evaluate the individual vertebral levels for artifacts 1
• Consider QCT (quantitative CT) when extensive degenerative changes are present, as it selectively samples only cancellous bone and excludes posterior elements 1

Inappropriate Use of T-Scores in Younger Patients

Never use T-scores or apply WHO criteria to premenopausal women or men <50 years. 1

• This leads to overdiagnosis and inappropriate treatment 1
• Always report Z-scores for this population 1

Peripheral vs. Central DXA

Peripheral bone density testing (forearm, heel) may identify higher-risk patients but requires confirmation with central DXA (spine and hip) for diagnosis. 1, 2

• Quantitative ultrasound (QUS) does not measure BMD and WHO definitions cannot be applied 1
• QUS is inappropriate for follow-up monitoring in all populations 1

Follow-Up and Monitoring Interpretation

A minimum 2-year interval between DXA scans is required to reliably detect true bone density changes due to precision limitations. 1, 4

When to Shorten Rescreening Intervals

• New glucocorticoid therapy or other medications causing bone loss 4
• Incident fragility fracture 4
• Development of conditions associated with secondary bone loss (hyperparathyroidism, hypogonadism, chronic inflammatory diseases) 4
• Significant weight loss, particularly if weight drops below 70 kg 4

When to Consider Longer Intervals

• Younger postmenopausal women (60-65 years) without additional risk factors 4
• Patients with normal or near-normal baseline BMD and no new risk factors 1, 4

Clinical Context for Treatment Decisions

For patients with T-score ≤-2.5, initiate oral bisphosphonates as first-line therapy. 2, 5, 6

For very high-risk patients (recent vertebral fracture, hip fracture with T-score ≤-2.5, multiple prevalent fractures), consider anabolic therapy (teriparatide, abaloparatide, or romosozumab) as initial treatment. 5, 6, 3

• All patients should receive calcium 1000-1200 mg daily and vitamin D 800-1000 IU daily 2, 5, 6
• Weight-bearing and resistance exercises reduce fracture risk independent of BMD changes 2, 5, 6