How is the FRAX (Fracture Risk Assessment) score calculated?

FRAX Score Calculation

The FRAX (Fracture Risk Assessment) tool calculates 10-year probability of hip fracture or major osteoporotic fracture for persons aged 40 to 90 years by using demographic and clinical factors alone or in combination with femoral neck BMD measurements. 1

Components of FRAX Calculation

FRAX incorporates the following key elements:

• Demographic factors:

  • Age (40-90 years)
  • Sex
  • Weight and height (BMI calculation)
  • Race/ethnicity (in country-specific versions)

• Clinical risk factors (binary yes/no inputs):

  • Previous fragility fracture
  • Parent with hip fracture
  • Current smoking
  • Glucocorticoid use
  • Rheumatoid arthritis
  • Secondary osteoporosis
  • Alcohol consumption (≥3 units/day)

• Optional BMD measurement:

  • Femoral neck BMD (T-score)

How FRAX Works

1. Country-specific calibration: FRAX uses country-specific fracture incidence and mortality data 1

2. Two calculation methods:

   • Without BMD: Using only clinical risk factors
   • With BMD: Incorporating femoral neck BMD for improved accuracy 1

3. Output:

   • 10-year probability of hip fracture
   • 10-year probability of major osteoporotic fracture (hip, clinical spine, humerus, or wrist)

Important Considerations

• Accuracy improvement: FRAX with BMD is more accurate than FRAX alone or BMD alone 1

• Race-specific versions: In the US, four different versions exist (Hispanic, non-Hispanic Asian, non-Hispanic Black, and non-Hispanic White) 1

• Glucocorticoid adjustment: For patients on glucocorticoids, the risk of major osteoporotic fracture should be increased by 1.15, and the risk of hip fracture by 1.2, if the prednisone dose is >7.5 mg/day 1

• Measurement accuracy: Self-reported height and weight can lead to significant errors in FRAX calculations; measured values should be used 2

Limitations of FRAX

• Binary inputs: FRAX uses yes/no inputs for factors like glucocorticoid and alcohol use rather than quantified dose exposure 1

• Limited factors: Does not include:

  • Lumbar spine BMD
  • Trabecular bone score
  • History of falls or frailty
  • Medical conditions like diabetes 1

• Age restrictions: Not validated for adults <40 years 3

• Underestimation in certain groups: FRAX may underestimate risk in patients with recent fractures, especially those younger than 65 years 4

Clinical Application

• For adults ≥40 years, FRAX should be calculated with BMD testing (if available) within 6 months of initiating assessment 1, 3

• A 65-year-old White female with no risk factors has a 9.3% 10-year risk for any osteoporotic fracture 1

• FRAX is incorporated into DXA software and electronic health record systems in many healthcare settings 1

• For patients on glucocorticoids, FRAX should be calculated with dose adjustment 1, 3

When to Use FRAX

• Most beneficial for patients with osteopenia (T-score between -1.0 and -2.5) to determine treatment necessity 5

• For patients with very high risk factors (age ≥70 with parent history of fracture or age ≥65 with previous fracture), treatment is typically indicated regardless of FRAX score 5

• Hip fracture risk prediction accounts for 98% of treatment indications, making it the most clinically relevant output 5

FRAX remains the most studied and widely implemented fracture risk assessment tool worldwide, incorporated into 120 guidelines and clinical decision support tools 1.