How to Calculate Osteoporotic Fracture Risk
Use the FRAX calculator (available online at www.shef.ac.uk/FRAX) to calculate 10-year probability of hip fracture and major osteoporotic fracture by entering patient age, sex, clinical risk factors, and femoral neck BMD T-score when available. 1
Primary Calculation Method: FRAX Tool
FRAX is the most studied and widely validated fracture risk assessment tool, incorporated into 120 guidelines worldwide and FDA-approved for integration into DXA software. 1 The calculator generates two key outputs:
- 10-year probability of hip fracture
- 10-year probability of major osteoporotic fracture (MOF) - includes clinical vertebral, hip, forearm, or humerus fractures 1
Required Input Variables
Enter the following data into the FRAX calculator 2, 3:
- Age (40-90 years)
- Sex
- Weight and height (to calculate BMI)
- Prior fragility fracture (yes/no)
- Parental history of hip fracture (yes/no)
- Current smoking (yes/no)
- Glucocorticoid use (yes/no - equivalent to ≥5 mg prednisone daily for >3 months)
- Rheumatoid arthritis (yes/no)
- Secondary osteoporosis (yes/no - includes conditions like inflammatory bowel disease, chronic liver/kidney disease)
- Alcohol consumption (≥3 units daily, yes/no)
- Femoral neck BMD T-score (optional but strongly recommended)
Critical Consideration: BMD Inclusion
Including femoral neck BMD significantly improves FRAX accuracy - predictions using FRAX plus BMD are more accurate than either FRAX alone or BMD alone. 1 Without BMD, FRAX may inappropriately recommend treatment for patients with normal bone density or miss treatment candidates with osteoporosis, particularly in younger patients with high BMI and low T-scores or older patients with normal T-scores. 4
Manual Adjustments for High-Dose Glucocorticoids
For patients taking prednisone >7.5 mg/day, manually adjust the calculated FRAX scores since the tool only captures glucocorticoid use as a binary yes/no variable 2, 3:
Treatment Thresholds Based on Calculated Risk
After calculating FRAX scores, apply these thresholds to determine treatment recommendations 1, 2:
Very High Fracture Risk (Consider Anabolic Therapy First)
- MOF risk >30% OR hip fracture risk >4.5% 1
- Recent fracture within past 12 months 1
- Multiple fractures 1
- T-score <-3.0 1
- Fractures while on osteoporosis therapy 1
High Fracture Risk (Consider Antiresorptive Therapy)
- MOF risk ≥20% OR hip fracture risk ≥3% 1, 2
- T-score ≤-2.5 at hip or spine 1
- Prior spine or hip fracture regardless of BMD 1
Intermediate Fracture Risk
- Age-dependent FRAX probability thresholds (varies by country-specific guidelines) 1
- T-score between -1.0 and -2.5 with MOF risk 10-20% or hip fracture risk 1-3% 1
Alternative Risk Assessment Tools
While FRAX is preferred, other validated tools include 1:
- Garvan Fracture Risk Calculator - calculates 5-year and 10-year risk, includes fall history (not captured by FRAX) 1
- Fracture Risk Calculator (FRC) 1
- CAROC (Canadian tool) 1
Important Limitations and Pitfalls
FRAX is only validated for untreated patients aged 40-90 years - do not use in patients <40 years, children, or those already on osteoporosis therapy. 3, 5 For younger adults on glucocorticoids, use clinical risk assessment with BMD Z-scores instead. 3
FRAX does not account for:
- Dose-dependent effects of glucocorticoids beyond yes/no 1, 2
- Fall history or frailty 2
- Lumbar spine BMD or trabecular bone score 2
- Number of prior fractures (only yes/no) 1
Race-specific FRAX calculators may underestimate risk in non-White populations since they use lower baseline fracture incidence data, potentially leading to disparities in treatment recommendations for patients with otherwise identical risk profiles. 1
Reassessment Intervals
Recalculate FRAX every 1-3 years for patients on glucocorticoids not receiving osteoporosis treatment, with earlier reassessment for very high-dose glucocorticoid users. 2, 5 For patients with osteopenia and low initial FRAX scores, repeat in 2 years or in 1 year if new risk factors develop. 2