Jaundice results when there is too much bilirubin in the body. There are several reasons why a cat may have excessive bilirubin, a condition that the veterinarian may refer to as hyperbilirubinemia. One cause is pre-hepatic icterus, in which there is so much bilirubin being produced that the liver is unable to process all of it. Pre-hepatic icterus often results from a breakdown of red blood cells due to the feline leukemia virus infection, defects in the blood clotting mechanism, and certain medications.
When a cat has an abnormal metabolism and excretion of bilirubin by its liver cells, it has the primary hepatic form of jaundice. Primary hepatic jaundice is the most common cause of icterus in the cat. Liver diseases that can affect cats include acute toxic hepatitis, cholangiohepatitis, cirrhosis of the liver, and feline fatty liver syndrome. Other diseases that result in damage to the liver -- such as diabetes mellitus, the feline infectious peritonitis virus, cancer, and the feline leukemia virus -- can also cause primary hepatic jaundice.
Finally, when the cat's bile duct system interferes with the excretion of bilirubin, a type of jaundice called post-hepatic icterus results. Causes of this include bile duct obstruction, a rupturing of the bile duct, pancreatitic disease, cancer, inflammation of the gallbladder, and inflammation of a bile duct.
