Standardization of ROC curve areas for diagnostic evaluation of liver fibrosis markers based on prevalences of fibrosis stages.

BACKGROUND The area under the ROC curve (AUC) is widely used as an estimate of the diagnostic value for fibrosis markers. Whether there is variability in the AUC related to the prevalence of fibrosis stages defining advanced and nonadvanced fibrosis is unknown. The aim of this study was to assess the relationships between the AUC and the prevalence of each fibrosis stage and to elaborate simple methods of standardization. METHODS The AUCs of FibroTest (FT) for the diagnosis of advanced fibrosis were estimated in patients with chronic hepatitis C using an integrated database including 1312 patients with FT and biopsy, and in an overview of 18 diagnostic studies. RESULTS In the integrated database considering stage prevalence, the FT AUC for advanced fibrosis varied (P <0.001) from 0.67 (only stage F2 as advanced fibrosis and only F1 as nonadvanced fibrosis) to 0.98 (only F4 as advanced fibrosis and only F0 as nonadvanced fibrosis). The same results were observed in the overview, in which the FT AUC varied (P <0.001) from 0.65 to 0.89 according to fibrosis stage prevalence. Two approaches for expressing standardized AUCs were developed: one approach assumed a uniform prevalence distribution of each fibrosis stage; the other approach used the prevalence distribution of fibrosis stages observed in the population. CONCLUSIONS The expressions of the AUCs of fibrosis markers should be standardized according to the prevalence of fibrosis stages defining advanced and nonadvanced fibrosis.