How is the Frax (Fracture Risk Assessment) score used to guide osteoporosis treatment?

How to Use the FRAX Score in Clinical Practice

Primary Purpose and Patient Selection

FRAX calculates 10-year absolute fracture probability to identify which patients with osteopenia or clinical risk factors should receive pharmacologic osteoporosis treatment, addressing the critical limitation that most fractures occur in patients with BMD T-scores above -2.5. 1

• Use FRAX for untreated postmenopausal women and men aged 40-90 years (or ≥50 years per National Osteoporosis Foundation guidance) 2, 3
• Do not use FRAX in adults <40 years, children, or patients already on osteoporosis therapy 1
• FRAX is validated only for treatment-naive patients, though it retains predictive value in treated populations for reassessment decisions 4

Required Input Variables

Enter the following into the online FRAX calculator 2:

• Patient demographics: Age, sex, weight, height (to calculate BMI)
• Femoral neck BMD T-score (optional but strongly recommended—omitting it leads to treatment discordance in 10.6% of cases, particularly in older patients with normal BMD and younger patients with high BMI) 5
• Seven clinical risk factors (dichotomous yes/no): 6, 2
  • Prior fragility fracture
  • Parental history of hip fracture
  • Current tobacco smoking
  • Long-term oral glucocorticoid use
  • Rheumatoid arthritis
  • Secondary causes of osteoporosis
  • Alcohol consumption ≥3 units/day

Treatment Decision Thresholds

Recommend pharmacologic treatment when FRAX demonstrates: 6, 1, 2

• ≥3% 10-year hip fracture risk, OR
• ≥20% 10-year major osteoporotic fracture risk (hip, clinical spine, humerus, or wrist)

For screening younger postmenopausal women (ages 50-64), the US Preventive Services Task Force uses a threshold equivalent to a 65-year-old white woman's baseline risk (9.3% 10-year major fracture probability) 6

Critical Glucocorticoid Adjustments

For patients on prednisone >7.5 mg/day, manually adjust the calculated FRAX scores: 6, 2

• Multiply major osteoporotic fracture risk by 1.15
• Multiply hip fracture risk by 1.2

This correction accounts for dose-dependent effects beyond the dichotomous glucocorticoid input, as FRAX assumes moderate-dose prednisone (2.5-7.5 mg/day) 6

Risk Stratification for Treatment Selection

Categorize patients into risk tiers to guide medication choice 6, 1:

• Very high risk (anabolic therapy consideration):

  • Fracture probability >1.2 times the intervention threshold, OR
  • ≥30% 10-year major osteoporotic fracture risk, OR
  • ≥4.5% 10-year hip fracture risk
  • Recent fracture within past 24 months (use FRAXplus with recency multipliers)
  • High-dose glucocorticoids (≥30 mg/day prednisone with cumulative dose >5 gm)
  • Multiple risk factor combinations

• High risk (oral bisphosphonates first-line):

  • Meets standard treatment thresholds (≥3% hip or ≥20% major fracture)
  • Single clinical risk factor with older age

Reassessment Intervals

For patients on continued glucocorticoids not receiving osteoporosis therapy: 1, 2

• Reassess FRAX every 1-2 years if low or moderate fracture risk
• Reassess earlier (within 1 year) for very high-dose glucocorticoid users or if new risk factors develop

For patients on osteoporosis treatment: 1

• Reassess FRAX every 1-2 years to determine if BMD is stable, improving, or declining
• Note that FRAX maintains predictive value in treated patients for guiding continuation or withdrawal decisions, though it should not be used to quantify treatment-induced risk reduction 4

Key Clinical Insights from Algorithm Analysis

Age and T-score are the strongest contributors to hip fracture risk, while BMI has marginal contribution. 7

• For women ≥65 years with a previous fracture, 98% of FRAX combinations exceed treatment threshold regardless of T-score or other factors 7
• For women ≥70 years with parental hip fracture history, 99% of FRAX combinations exceed treatment threshold 7
• Hip fracture risk prediction accounts for 98% of treatment indications; major osteoporotic fracture risk adds minimal additional treatment recommendations 7

Critical Limitations and Pitfalls

FRAX has important constraints that require clinical judgment: 6, 1

• Uses binary glucocorticoid exposure (yes/no) rather than quantified dose—requires manual adjustment for high doses
• Does not incorporate lumbar spine BMD or trabecular bone score
• Lacks information about fall history or frailty
• Race-specific calculators may perpetuate disparities (Asian, Black, and Hispanic versions always generate lower risk than White versions for identical clinical profiles)
• Based on cohort studies 30-40 years old with mortality estimates from 2004
• Does not account for diabetes or other medical conditions affecting bone quality

Common pitfall: Using FRAX in younger adults (<40 years) where it is not validated—instead use BMD Z-scores and clinical risk assessment for this population 6, 1