What are the guidelines for performing a Dual-Energy X-ray Absorptiometry (DEXA) scan to assess bone mineral density in patients at risk of osteoporosis?

DEXA Scan Guidelines for Osteoporosis Screening

Dual-Energy X-ray Absorptiometry (DEXA) scanning should be performed for all women aged 65 and older and men aged 70 and older, with earlier screening for individuals with significant risk factors for osteoporosis. 1, 2

Who Should Receive DEXA Scans

Universal Screening

• Women age 65 years and older
• Men age 70 years and older 1, 2

Earlier Screening for High-Risk Individuals

• Women younger than 65 years with risk factors:

  • Estrogen deficiency
  • Maternal hip fracture history after age 50
  • Low body weight (<127 lb or 57.6 kg)
  • History of amenorrhea (>1 year before age 42) 1

• Additional risk factors for both men and women:

  • Current smoking
  • Loss of height, thoracic kyphosis
  • Chronic inflammatory conditions
  • Glucocorticoid therapy (>3 months)
  • Hypogonadism
  • Medications known to affect bone density (PPIs, anticoagulants, certain antidepressants)
  • Malabsorption or malnutrition
  • Organ transplantation
  • Prolonged immobilization
  • Endocrine disorders affecting bone 1, 2

• Individuals of any age with:

  • Bone mass osteopenia or fragility fractures on imaging
  • Fractures with minimal trauma (wrist, hip, spine, proximal humerus) after age 50
  • One or more insufficiency fractures 1

Recommended Imaging Protocol

Standard Protocol

• DXA of the lumbar spine and hip(s) is the gold standard with highest rating (9/9) for appropriateness 1
• Standard screening should include:
  • Posteroanterior spine
  • Total hip
  • Femoral neck 2

Special Situations

• Forearm DXA when:

  • Hip/spine cannot be measured or interpreted
  • Primary or secondary hyperparathyroidism
  • Patient exceeds weight limit for DXA table 1

• QCT (Quantitative CT) when:

  • Advanced degenerative changes of the spine are present (rated 8/9 for appropriateness)
  • Scoliosis is present 1

Interpretation of Results

• WHO definitions:

  • Normal: T-score > -1.0
  • Osteopenia: T-score between -1.0 and -2.4
  • Osteoporosis: T-score ≤ -2.5 1, 2

• Use Z-scores (not T-scores) for:

  • Premenopausal women
  • Men under 50
  • Children and adolescents 2

• Z-scores ≤ -2.0 are considered below expected range for age 1

Follow-up Intervals

• Standard monitoring interval: 2 years 1, 2
• Shorter intervals (1 year) for:
  • Patients initiating osteoporosis therapy
  • Patients at high risk for rapid bone loss (e.g., glucocorticoid therapy)
  • After cessation of pharmacologic therapy 1
• Scan intervals <1 year are discouraged 1

Important Technical Considerations

• Patients should be scanned on the same DXA machine for follow-up 1, 2
• Compare BMD values (not T-scores) between previous and current scans 1, 2
• Daily phantom scans are recommended for quality control 2
• Each facility should determine precision error and calculate least significant change (LSC) 2

Common Pitfalls to Avoid

• False elevations in BMD readings due to:

  • Osteoarthritis
  • Calcification of the aorta
  • Advanced degenerative changes of the spine 2

• Misinterpretation in special populations:

  • Using T-scores instead of Z-scores for premenopausal women
  • Not accounting for vertebral fractures (which may indicate osteoporosis regardless of BMD)
  • Failure to recognize secondary causes of osteoporosis 1, 2

• Visual assessment of X-rays is not reliable for diagnosing osteoporosis (only 49% accuracy compared to DEXA) 3

Treatment Decisions Based on DEXA Results

• Treatment recommended for:
  • T-score ≤ -2.5 (osteoporosis)
  • Fragility fracture regardless of T-score
  • Osteopenia (T-score -1.0 to -2.4) with 10-year hip fracture risk ≥3% or major osteoporotic fracture risk ≥20% based on FRAX 1, 4
  • Glucocorticoid-induced osteoporosis with T-score < -1.5 5

DEXA remains the most reliable method for diagnosing osteoporosis and assessing fracture risk, with proven ability to predict fracture risk and guide appropriate treatment decisions 6.