FRAX Score Calculation Components
The FRAX score is calculated using demographic factors (age, sex, weight, height, and race/ethnicity) and clinical risk factors including previous fragility fracture, parental history of hip fracture, current smoking status, glucocorticoid use, rheumatoid arthritis, secondary osteoporosis, and alcohol consumption, with optional inclusion of femoral neck bone mineral density (BMD). 1
Core Components of FRAX Calculation
The FRAX tool incorporates the following factors:
Demographic Factors:
- Age (40-90 years)
- Sex
- Weight and height (used to calculate BMI)
- Race/ethnicity (country-specific)
Clinical Risk Factors:
- Previous fragility fracture
- Parental history of hip fracture
- Current smoking status
- Long-term use of oral glucocorticoids (>3 months)
- Rheumatoid arthritis
- Secondary causes of osteoporosis
- Alcohol consumption (≥3 units daily)
- Femoral neck BMD (optional but improves accuracy) 1, 2
Output and Interpretation
The FRAX calculation provides two key outputs:
- 10-year probability of hip fracture
- 10-year probability of major osteoporotic fracture (hip, clinical spine, humerus, or wrist)
These probabilities are expressed as percentages and are used to guide treatment decisions. The National Osteoporosis Foundation recommends treatment for patients with:
- 10-year probability of hip fracture ≥3%, or
- 10-year probability of major osteoporotic fracture ≥20% 2, 1
Important Considerations and Limitations
Glucocorticoid Adjustment
For patients on glucocorticoids at doses >7.5 mg/day of prednisone, FRAX underestimates risk. The calculated risk should be increased by:
- 15% for major osteoporotic fracture
- 20% for hip fracture 1
Age Restrictions
- FRAX is not validated for adults under 40 years of age 1
- The algorithm is designed for use in previously untreated postmenopausal women and men 40 to 90 years of age 2
Country-Specific Calculations
FRAX uses country-specific fracture incidence and mortality data, making the tool more accurate for the population being assessed 1, 3
Relative Contribution of Factors
Research has shown that age and T-score (when BMD is included) are the strongest contributors to hip fracture risk, while BMI has a marginal contribution. Among clinical risk factors, parental history of hip fracture and ongoing glucocorticoid treatment have the largest additive effects on risk score 3
Clinical Application
FRAX provides a more comprehensive assessment of fracture risk than BMD alone by incorporating clinical risk factors that are partly independent of BMD. This allows for more informed treatment decisions, especially in patients with osteopenia (T-scores between -1.0 and -2.5) 2, 1
For certain high-risk populations, FRAX calculation may be unnecessary:
- 98% of women 65 years and older with a previous fracture exceed treatment thresholds regardless of T-score or other factors
- 99% of women age 70+ with a parent history of hip fracture exceed treatment thresholds 3
By providing standardized fracture risk assessment, FRAX helps clinicians identify patients who would benefit most from pharmacologic intervention, ultimately reducing the burden of osteoporotic fractures.