Understanding the FRAX Fracture Risk Assessment Tool
The Fracture Risk Assessment Tool (FRAX®) was developed by the World Health Organization (WHO) Collaborating Centre for Metabolic Bone Diseases at the University of Sheffield. It integrates individual clinical risk factors and, optionally, femoral neck bone mineral density (BMD) to estimate the 10‑year probability of a major osteoporotic fracture (clinical spine, hip, forearm, or shoulder fracture) and a hip fracture specifically.
FRAX is endorsed by major professional societies including the American Association of Clinical Endocrinologists (AACE), the Endocrine Society, the National Osteoporosis Foundation (NOF), and the International Osteoporosis Foundation (IOF). It is widely used in primary care, endocrinology, rheumatology, and orthopedics to guide decisions about osteoporosis screening and pharmacologic therapy.
Core principle: FRAX uses a Cox proportional‑hazards model derived from population‑based cohorts (including the Rotterdam Study, the EPIDOS Study, the Study of Osteoporotic Fractures, and the CaMos Study). The algorithm outputs absolute 10‑year fracture risk, which can be combined with country‑specific mortality estimates.
The Clinical Risk Factors in FRAX
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Age & Sex – The strongest predictors; risk increases exponentially with age.
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BMI – Low BMI (≤ 20 kg/m²) is an independent risk factor.
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Prior fragility fracture – A history of fracture after age 40 doubles future fracture risk.
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Parental hip fracture – Reflects genetic and environmental determinants of bone strength.
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Current smoking – Tobacco use increases fracture risk through multiple mechanisms (reduced bone mass, impaired healing, altered estrogen metabolism).
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Glucocorticoid use – ≥5 mg/day prednisolone (or equivalent) for ≥3 months; dose‑ and duration‑dependent effect.
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Rheumatoid arthritis – Systemic inflammation and immobility contribute to bone loss.
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Secondary osteoporosis – Conditions such as type 1 diabetes, hypogonadism, malabsorption, chronic liver disease, and hyperthyroidism.
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Alcohol intake – ≥3 units/day (approx. 30 g alcohol/day) is associated with reduced bone quality and increased fall risk.
Bone Mineral Density (BMD) in FRAX
Including femoral neck BMD (measured by DXA) refines the risk estimate. The FRAX algorithm uses the BMD value directly (in g/cm²) rather than T‑score. However, many clinicians and patients are familiar with T‑scores: a T‑score ≤ −2.5 at the femoral neck indicates osteoporosis. In the FRAX model, each unit decrease in BMD (approximately 1 SD) approximately doubles the fracture risk. The calculator optionally computes an estimated T‑score using the NHANES III reference database for femoral neck BMD in women and men, and an age‑adjusted Z‑score for peer comparison.
Clinical Case: 68‑Year‑Old Woman with Multiple Risk Factors
A 68‑year‑old postmenopausal woman (BMI 22 kg/m²) with a prior wrist fracture, a mother who fractured her hip at age 78, and current smoking presents for evaluation. Her femoral neck BMD is 0.68 g/cm² (T‑score −2.6). FRAX calculates a 10‑year major osteoporotic fracture risk of 28% and a hip fracture risk of 9.5%. According to the NOF guidelines, a major fracture risk ≥20% or hip fracture risk ≥3% is an intervention threshold, and the clinician recommends pharmacologic therapy (e.g., bisphosphonate) along with lifestyle modifications and falls prevention.
This case illustrates the value of FRAX in integrating multiple risk factors beyond BMD alone.
Interpreting the Results
FRAX outputs absolute risks (percentages) for the next 10 years. There is no single "normal" value; risk thresholds vary by country and clinical context. In the United States, the National Osteoporosis Foundation (NOF) recommends considering pharmacologic treatment when:
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10‑year major osteoporotic fracture risk ≥ 20%, or
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10‑year hip fracture risk ≥ 3%.
In the UK, the National Institute for Health and Care Excellence (NICE) suggests an intervention threshold of ≥10% for major fractures. Clinicians should use their judgment and consider individual patient preferences, comorbidities, life expectancy, and values.
Common Misconceptions
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"FRAX is only for women." – FRAX includes sex‑specific models and is validated for both men and women.
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"FRAX requires BMD." – BMD is optional; the tool works with clinical risk factors alone, although BMD improves precision.
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"A low risk means I don't need to worry." – Risk is a continuum; low absolute risk does not exclude the possibility of fracture, and lifestyle measures remain important.
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"FRAX is a diagnostic test." – FRAX is a risk assessment tool, not a diagnostic test for osteoporosis. BMD testing and clinical evaluation remain essential.
Validation and Evidence Base
The FRAX algorithm has been validated in more than 30 independent cohorts from Europe, North America, Asia, and Australia, encompassing over 2 million person‑years of follow‑up. It has been shown to outperform BMD alone in predicting fractures, particularly hip fractures. The model is continuously updated by the WHO Collaborating Centre. The version used in this calculator is based on the FRAX® v4.1 algorithm (2023 update) with U.S. Caucasian reference data, adaptable to other ethnicities via country‑specific calibration.
Key references include:
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Kanis JA, et al. (2008) "FRAX™ and the assessment of fracture probability in men and women from the UK." Osteoporos Int 19(4):385‑397.
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Watts NB, et al. (2010) "National Osteoporosis Foundation 2008 Clinician's Guide to Prevention and Treatment of Osteoporosis." Osteoporos Int 21(1):1‑20.
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Compston J, et al. (2017) "UK clinical guideline for the prevention and treatment of osteoporosis." Arch Osteoporos 12(1):43.
Step‑by‑Step Use of the Calculator
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Enter the patient's age (40‑90 years), sex, weight, and height (BMI is auto‑calculated).
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Select all applicable clinical risk factors from the checklist.
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Optionally, check the box to include femoral neck BMD and enter a value (g/cm²).
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Click "Calculate 10‑Year Risk" to obtain the estimates.
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Review the results, including risk categorization (low, moderate, high), contribution breakdown, and the 10‑year risk trajectory chart.
Frequently Asked Questions
What is the difference between major osteoporotic fracture and hip fracture risk?
Major osteoporotic fracture includes fractures of the spine, hip, forearm, and shoulder – the most common fragility fractures. Hip fracture is a subset and is often the most clinically severe, with high morbidity and mortality. FRAX provides both estimates separately because hip fracture has a distinct risk profile.
Do I need a DXA scan to use FRAX?
No. FRAX can be used with clinical risk factors alone. However, including femoral neck BMD (if available) improves the accuracy of the risk estimate, especially in individuals with borderline risk.
Is FRAX applicable to all ethnicities?
Yes, FRAX includes country‑specific calibration for many countries and ethnic groups. This calculator includes a country/region selector (US, UK, Europe, Asia, Canada, Australia, China, Japan, South Africa, France) that adjusts baseline risks to better match local populations.
How often should FRAX be reassessed?
Generally, FRAX should be reassessed when there is a significant change in clinical status (e.g., new fracture, change in medication, substantial weight loss, or a new diagnosis causing secondary osteoporosis). Some guidelines suggest reassessment every 2‑5 years in older adults.
What is the intervention threshold for pharmacotherapy?
Thresholds vary by country and guideline. In the U.S., NOF suggests treatment if major fracture risk ≥20% or hip fracture risk ≥3%. In the UK, NICE recommends ≥10% for major fractures. Clinicians should consider patient preferences and comorbidities.
Can FRAX be used for patients under 40 or over 90?
FRAX is validated for ages 40‑90. For patients outside this range, the tool may not provide reliable estimates. For younger patients, clinical judgment and BMD are more appropriate. For those over 90, the risk is generally very high and treatment decisions are based on comorbidities and life expectancy.