A number of absolute fracture risk calculators are now available. These aim to better estimate an individual’s fracture risk by taking into account age and clinical risk factors as well as BMD, and have the potential to allow more effective targeting of therapy for osteoporosis. In Australia, the most common absolute fracture risk calculators in use are the following:
- Garvan Fracture Risk Calculator (GFRC). The GFRC was developed in Australia using data from the Dubbo
Osteoporosis Epidemiology Study.2,3
- Fracture Risk Assessment Tool (FRAX). FRAX uses data from nine epidemiological studies as well as the results of the placebo arms of clinical trials to estimate absolute fracture risk.4,5 Dual energy X-ray absorptiometry (DXA) scanners that incorporate specialised software have the ability to provide a FRAX estimate of absolute fracture risk.
While aiming to achieve the same outputs, FRAX and GFRC use different algorithms to estimate absolute fracture risk. The FRAX algorithm uses 13 risk factors, while GFRC uses five (Table 4). More variables however do not necessarily improve prediction, and fracture-risk calculators with five or fewer variables have been shown to perform as well as those with more variables.6 Both FRAX and GRFC can be used to calculate absolute fracture risk when BMD measurement is not available, because BMD is largely determined by age and weight. The different algorithms do result in different estimates of absolute fracture risk. FRAX was developed using multinational epidemiological data, and as such provides a country-specific fracture risk that takes into to account different baseline fracture and mortality rates. If a particular country is not available, FRAX recommends the use of the country most similar to the patient’s background.
There are a number of other differences between FRAX and GFRC:
- FRAX predicts ‘major osteoporotic fractures’, categorised as clinical spine, hip, forearm or shoulder fracture. GFRC predicts any osteoporotic fracture.
- FRAX determines an individual’s fracture risk over a 10-year period, while GFRC provides both five- and 10-year fracture predictions.
- FRAX links to a website that can adjust fracture risk estimate based on the patient’s trabecular bone score.
- Both FRAX and GFRC are available online. FRAX is also available as part of the latest DXA software from all DXA scanner manufacturers and is therefore more readily accessible at the present time.
The FRAX and GFRC calculators both have limitations:
- Falls as a risk factor for fracture is not included in the FRAX calculator. Falls risk is, however, recognised as an independent risk factor for fracture. Falls and number of falls are included in the GFRC.
- The FRAX questionnaire provides a number of risk factors as binary variables (yes/no) and does not allow graduations in exposure to risk factors, including prior fractures, smoking, alcohol use and glucocorticoid use.
- FRAX calculates a 10-year fracture risk for hip fracture and the combined group of ‘major osteoporotic’ fractures. Many other fractures, including rib, other femur, tibia and fibular fractures, are excluded.
- GFRC uses fewer risk factors and does not include known variables which increase fracture risk (ie family history of fracture).
- GFRC was determined from a broad based Australian population of mixed ethnicity, predominantly Caucasian. Its applicability to other racial groups and to immigrants who have spent a significant period of their lives overseas is uncertain. GFRC has, however, been validated in a number of international populations, including Canada, the Netherlands and Poland.7,8