Bile Acids, Direct Bilirubin and Gamma-glutamyltransferase as Prognostic Indicators for Horses with Liver Disease in the Eastern United States: 82 Cases (1997-2019).

Abstract Serum biochemistry results and presence of fibrosis on liver biopsies are frequently used as prognostic indicators in horses with liver dysfunction. The objective of this retrospective multicenter study was to determine if the magnitude of abnormal liver specific biochemical tests such as bile acids (BA), direct bilirubin and gamma-glutamyltransferase (GGT), or the presence of fibrosis reported on liver biopsies was associated with prognosis in horses with liver dysfunction. Eighty-two horses older than one year, examined at four referral hospitals in the eastern United States, with BA values greater than 30 µmol/L and having 6-months or more follow-up were included in the study. The association of the maximal BA, GGT and direct bilirubin values of each horse with survival was determined by logistic regression analysis. The presence or absence of fibrosis (non-quantitated) on a liver biopsy was compared between survivors and non-survivors by chi square test. The degree of increase in BA concentration and GGT activity was not related to outcome (OR 0.9999, 95% CI 0.9923 – 1.007, P = 0.97, and OR 1.0, 95% CI 0.9997 – 1.001, P = 0.31 respectively). Direct bilirubin concentration was positively associated with non-survival (OR 1.95, 95% CI 1.34-3.19, P = 0.0023). The presence of fibrosis was not associated with outcome (P = 0.37). These findings suggest that the magnitude of GGT and BA values or the mere presence of fibrosis on liver histopathology should not be used as prognostic indicators. In this study, direct bilirubin values were a better predictor of outcome.