Evaluation of bile acids and bilirubin in serum and abdominal fluid in dogs with abdominal effusion.

Objectives: Determine the utility of abdominal fluid bile acids concentration to diagnose biliary tract rupture and the utility of abdominal fluid-to-serum bilirubin ratio as diagnostic tools in dogs.

Materials and methods: This was a prospective pilot study. Canine serum and abdominal fluid samples were collected and submitted for the determination of bilirubin and bile acids concentrations between 2020 and 2022. Samples were measured at the time of admission from dogs with acute onset of clinical signs and peritoneal fluid. A Mann-Whitney U test and ROC curves were used to compare serum and abdominal fluid bilirubin and bile acids concentration and fluid-to-serum bilirubin and bile acids ratio between patients with biliary tract rupture and non-biliary tract rupture.

Results: Ninety-four cases were included, of which seven were diagnosed with biliary tract rupture. Median abdominal fluid bile acids concentration was significantly higher in dogs with biliary tract rupture than non-biliary tract rupture (P-value <0.001). Abdominal fluid bile acids concentration had a sensitivity of 100% and specificity of 99% for the diagnosis of biliary tract rupture. Fluid-to-serum bilirubin ratio was also analysed and no statistically significant difference was seen between groups (P-value 0.925).

Clinical significance: Although the number of dogs with biliary tract rupture in this study population was small, abdominal fluid bile acids concentration may have a better accuracy than fluid-to-serum bilirubin ratio for the diagnosis of biliary tract rupture. The utility of fluid-to-serum bilirubin ratio for the diagnosis of biliary tract rupture, appears limited. Further studies with a larger number of biliary tract rupture cases are required to support these conclusions.