Congress on Demand 2021: Internal Medicine

The cat presenting with jaundice is rewarding to investigate because it already gives us a strong clue as to where its disease may be and there are a limited number of differentials for jaundice. Obviously, the cat is yellow because of increased circulating bilirubin. Considering the normal metabolism and pathway of bilirubin production and breakdown reminds us of pre-hepatic, hepatic and post-hepatic causes which need to be differentiated. Prehepatic jaundice is caused by increased production of bilirubin exceeding the capacity for hepatic excretion due to red blood cell destruction. It is distinguished from the others by a low haematocrit but icterus is very unlikely to occur unless anaemia is severe. Hepatic jaundice is associated with impaired hepatic uptake, conjugation or excretion into bile and occurs with hepatic disorders in which severe intrahepatic cholestasis develops, e.g. inflammatory liver diseases and feline hepatic lipidosis. Post-hepatic jaundice is associated with interruptions in flow in the extrahepatic bile ducts such as with choleliths; pancreatitis and biliary tract infection. Careful investigation with a combination of blood samples, ultrasonography, bile aspirates and (when indicated) liver biopsies should allow effective diagnosis and treatment.