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FRAX: Read the Two Probabilities Without Adding Them

Interpret overlapping fracture probabilities and US treatment thresholds without adding risks or replicating FRAX.

Quick Medical Calculator Editorial Team · Reading label · 2 min read

Retrospective study sequence, not publication date

Editorial record

This source-linked educational article has been updated through AI-assisted evidence checks and editorial review. Verify information against current guidance and local protocols before applying it to patient care.

Citation methodology

FRAX reports 10-year probabilities of hip fracture and major osteoporotic fracture (MOF). MOF includes hip, clinical spine, forearm, and proximal humerus fractures. These are overlapping outcomes, not two separate risks to add together. BHOF clinician's guide.

Validate the Report Before the Threshold

Record the country model, age, relevant history, and whether femoral-neck bone mineral density was included. The standard tool accepts ages 40-90. Do not substitute a lumbar-spine T-score for its femoral-neck input or assume that a country choice is merely a display preference. Country calibration affects absolute probability. Official calculator, FRAX developer FAQ.

Use an authorized FRAX implementation. This article does not provide a substitute formula or claim to validate a site's implementation of the proprietary model.

Worked Interpretation, Not a Simulated FRAX Calculation

Suppose a report for a fictional US postmenopausal patient with osteopenia gives MOF 18% and hip 3.2%. These values are invented solely to demonstrate interpretation; they were not generated from a patient dataset.

  • Do not report a "combined risk" of 21.2%: hip fractures already contribute to MOF.
  • The hip probability meets the US BHOF intervention threshold even though MOF is below 20%.
  • That supports a treatment discussion, not selection of a particular drug without assessment.

BHOF's US framework applies to postmenopausal women and men aged 50 or older. In people with low bone mass at the hip, it uses hip probability at least 3% or MOF probability at least 20%. Hip or vertebral fracture and osteoporosis-range BMD can create treatment indications independently of those FRAX thresholds. These are not worldwide treatment rules. BHOF guide.

What a Modest Probability May Miss

The base model simplifies several exposures. Fracture recency and number, glucocorticoid dose, and falls can alter the clinical picture. FRAXplus offers defined adjustments for additional information; do not stack informal corrections or claim the adjustment resolves every limitation. FRAX is also not sufficiently sensitive to serve as a treatment-response target. Developer FAQ.

A useful note therefore contains both probabilities, their time horizon, the model and BMD site, relevant omitted risk factors, and the treatment framework used. A number below threshold should not stop a separate evaluation of a recent fragility fracture or recurrent falls.