Calculation of APRI and GPR for prediction of cystic fibrosis-related liver disease

Both APRI and GPR can be used to help predict fibrosis in CFLD. Interpretation depends on the upper limits of normal used for AST and GGT, respectively, which are not well standardized and vary among laboratories and age groups. In 1 study, APRI >0.26 was a good predictor of CFLD on liver biopsy (this study used 40 U/L as the upper limit of normal for ALT)^[1]. In another study, GPR of >0.2 predicted moderate hepatic fibrosis and GPR >0.6 predicted more advanced fibrosis (this study used 24 U/L as the upper limit of normal for GGT)^[2].

For these calculations, we suggest using the upper limits of normal from the CALIPER study, though these are age- and assay-specific and may differ from local laboratory upper limits of normal^[3]. Alternatively, it is reasonable to do these calculations using the following upper limits of normal: AST 30 U/L, GGT 21 U/L.