MedWire News: A World Health Organization (WHO) screening tool underestimates the risk for major osteoporotic fractures in Spanish patients, research shows.

The WHO fracture risk assessment tool (FRAX) effectively estimated the risk for hip fractures in the Spanish population, but the discriminatory ability of FRAX was modest, say Jesús González-Macias (University of Cantabria, Santander, Spain) and colleagues.

The FRAX algorithms are based on large population-based cohorts and calculate the 10-year risk for a major osteoporotic fracture and hip fracture adjusted for the fracture and death hazards of several countries, including Spain.

However, no Spanish cohorts were included in the analyses that led to the development of the FRAX algorithm.

Although FRAX is quickly becoming the gold standard among fracture risk models, "some aspects of its first adaptation to certain particular countries may introduce some miscalculation in the estimation of the fracture risks," say the researchers.

Using patient data from a large study conducted in Spain, González-Macias and colleagues compared the FRAX predicted risk for hip and major osteoporotic fractures with the actual fracture rate in the study.

In the journal Bone, they report that 0.96% of the 5201 women in the trial developed a major osteoporotic fracture and 3.81% of women presented with an incident hip fracture.

Overall, the ratio of the estimated 3-year risk for fracture versus the observed number of fractures (E/O ratio) was 1.10 and 0.66 for major and hip fractures, respectively.

The difference between the estimated and observed fracture cases reached statistical significance, "indicating that the Spanish FRAX algorithms have a limited predictive ability," according to the researchers.

Further analyses also revealed that the prediction tool had only modest overall discriminative ability for major osteoporotic and hip fractures, with an area under the ROC curve of 0.615 and 0.640 for major and hip fractures, respectively.

The researchers say an "indiscriminate, non-critical use of the tool" could have important clinical implications, particularly if at-risk women in Spain do not receive appropriate treatment as a result of the underestimation of risk.

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