FRAX tool ‘resistant’ to osteoporosis treatment effects

By Laura Cowen

Osteoporosis therapy does not invalidate the use of the World Health Organization's fracture risk assessment system (FRAX) for fracture prediction, study findings indicate.

The impact of osteoporosis therapy on 10-year fracture prediction with FRAX, and more specifically whether osteoporosis therapy invalidates use of FRAX for fracture prediction is unknown, explain William Leslie (University of Manitoba, Winnipeg, Canada) and colleagues in the Journal of Bone and Mineral Research.

To investigate, Leslie and team applied FRAX to 35,764 women aged 50 years and older who underwent BMD testing between 1996 and 2007.

A provincial pharmacy database was used to identify the women who had never been treated for osteoporosis (untreated; n=12,450), and treated patients who were current high adherence users (medication possession ratio [MPR] ≥0.80 in the year after BMD testing; n=9712), current low adherence users (MPR <0.80; n=9126), and past users (n=4476).

The team also assessed fracture outcomes to 10 years using hospital discharge data and physician billing claims. They found that during a mean 5.3 years of observation, 2276 individuals sustained incident major osteoporotic fractures, of which 474 were hip fractures.

Area under the receiver operating characteristic curve analysis showed that FRAX probabilities were similar among the treated and untreated patients. "There was no evidence that fracture discrimination in the treated subgroups was inferior to that found in untreated women," say the researchers.

Furthermore, concordance plots for major osteoporotic fractures and hip fractures showed good agreement between the predicted and observed 10-year fracture incidence in untreated women and in each treated subgroup.

When the team conducted a subgroup analysis among women with high adherence to at least 5 years of one type of bone resorption inhibitor (n=3047) they found that FRAX overestimated hip fracture, but not major osteoporotic fracture, in women in the highest tertile of FRAX-predicted risk.

The observed treatment effect in this high-risk tertile was similar to the risk reduction reported in clinical trials of this agent, Leslie et al note.

They conclude that their findings "potentially expand the clinical role of FRAX as a tool for advising patients on their need for continued treatment, and whether treatment could potentially be withdrawn."

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