How do I calculate the Fracture Risk Assessment (FRAX) score?

How to Calculate the FRAX Score

The FRAX score is calculated using the WHO online calculator (available at www.shef.ac.uk/FRAX/) by entering patient age, sex, clinical risk factors, and optionally femoral neck BMD T-score to generate a 10-year probability of hip fracture and major osteoporotic fracture. 1

Required Input Variables

Mandatory Information

• Age: Must be between 40-90 years 2
• Sex: Male or female 1
• Weight and Height: Used to calculate body mass index (BMI) 1
• Country/Ethnicity: Select appropriate population (U.S. versions include white, black, Asian, and Hispanic populations) 1

Clinical Risk Factors (Dichotomous Yes/No)

• Prior fragility fracture: Any previous low-trauma fracture 1
• Parental hip fracture history: Hip fracture in mother or father 1
• Current tobacco smoking 1
• Glucocorticoid use: Long-term oral glucocorticoid therapy 1
• Rheumatoid arthritis 1
• Secondary osteoporosis: Including hypogonadism and premature menopause 1
• Alcohol consumption: 3 or more units daily 1

Optional But Recommended

• Femoral neck BMD T-score: Including this significantly improves prediction accuracy and should be used for optimal application of FRAX 3, 2

Step-by-Step Calculation Process

1. Access the online tool at the WHO FRAX website and select the appropriate country-specific calculator 1

2. Enter demographic data: Input age, sex, weight, and height 2

3. Answer all clinical risk factor questions with yes/no responses 1

4. Input femoral neck BMD T-score if available from DXA scan (this is optional but strongly recommended to avoid treatment errors in specific patient subgroups) 3

5. Calculate: The tool automatically generates two outputs:

   • 10-year probability of major osteoporotic fracture (hip, clinical spine, humerus, or wrist) 1
   • 10-year probability of hip fracture 1

Critical Considerations When Using FRAX

When BMD Should Be Included

Always include the femoral neck T-score when available because FRAX without BMD can lead to inappropriate treatment recommendations in two specific subgroups: older patients with normal BMD may be overtreated, and younger patients with high BMI and low BMD may be undertreated 3. Agreement between FRAX with and without BMD is only 89.4%, with clinically significant disagreement in 10.6% of cases 3.

Validated Patient Population

• Postmenopausal women and men aged 50 years and older 1
• Intended for untreated patients only (not validated for those already on osteoporosis therapy) 1, 2
• Not validated for patients under 40 years of age 4

Special Adjustments for Glucocorticoid Users

For patients on glucocorticoids with prednisone dose >7.5 mg/day, manually adjust the calculated FRAX scores by multiplying major osteoporotic fracture risk by 1.15 and hip fracture risk by 1.2 4. This adjustment should be performed within 6 months of starting glucocorticoid therapy 4.

Interpreting Results and Treatment Thresholds

National Osteoporosis Foundation Treatment Thresholds

Pharmacologic treatment is recommended when:

• 10-year probability of hip fracture ≥3% OR 4, 5
• 10-year probability of major osteoporotic fracture ≥20% 4, 5

These thresholds apply specifically to patients with osteopenia (T-score between -1.0 and -2.5) to identify the subset who would benefit from treatment 2.

Limitations to Recognize

• Does not account for dose-dependent effects of glucocorticoids beyond the dichotomous yes/no input 4
• Does not capture fall risk, which requires separate clinical assessment 2
• Race-specific calculations may differ for patients with otherwise identical risk profiles 4
• Does not include number of prior fractures, only whether any prior fracture occurred 1

Reassessment Intervals

• For patients on glucocorticoids not receiving osteoporosis treatment: Recalculate FRAX every 1-3 years, with earlier reassessment for very high-dose glucocorticoid users 4
• For patients with osteopenia and low initial FRAX scores: Repeat in 2 years, or in 1 year if new risk factors develop 5