Measurement of abdominal fluid bilirubin concentration frequently fails to detect biliary tract rupture in dogs with gallbladder mucocele

Objective: To evaluate the diagnostic utility of abdominal fluid bilirubin concentration-to-serum bilirubin concentration ratio (AFB:SB) measurement in detecting biliary tract rupture or leakage in dogs with gallbladder mucocele (GBM; GBM group) versus no GBM (non-GBM group). Methods: For this retrospective cross-sectional study, a search of medical records identified dogs with concurrent measurements of abdominal fluid bilirubin and serum bilirubin concentrations prior to surgery or postmortem examination for biliary tract rupture or leakage between July 1, 2007, and January 31, 2022. Results for AFB:SB and other variables of interest were compared between the GBM versus non-GBM group and those with versus without biliary tract rupture or leakage. Results: 29 dogs were included (GBM group, n = 12; non-GBM, n = 17). Eleven GBM dogs and 7 non-GBM dogs had biliary tract rupture or leakage. The AFB:SB was > 2 for 2 of 11 (18%) GBM dogs with rupture, 6 of 7 (86%) non-GBM dogs with biliary tract rupture or leakage, and 2 non-GBM dogs without identified rupture/leakage. Abdominal fluid cytology confirmed the presence of bile in all dogs with a ruptured GBM. Conclusions: The use of AFB:SB alone frequently fails to detect biliary tract rupture or leakage in dogs with GBM; however, cytological analysis of abdominal fluid is valuable in helping to detect potential GBM rupture. Clinical Relevance: It is essential that primary care and emergency veterinarians be aware that an AFB:SB > 2 can be indicative of biliary tract rupture or leakage in dogs; however, the ratio may not be > 2 in dogs with ruptured GBM.