Jaundice (icterus), a yellow discoloration of tissues in the body, is caused by an increase of bilirubin in the blood-stream. Bilirubin is a breakdown product of red blood cell destruction. Jaundice is not a disease itself; rather, it is a symptom caused by a number of diseases that can be categorized as pre-hepatic (hemolytic), hepatic (liver disease), or post-hepatic (biliary stasis).
Pre-hepatic jaundice is caused by rapid red blood cell destruction as in the case of immune-mediated hemolytic anemia (IMHA), tick-borne disease, and drug toxicity. Red blood cells are being destroyed and bilirubin is being released into the blood-stream faster than the liver can metabolize and excrete it through the bile duct. Anemia is associated with this type of jaundice, and the cause of the anemia should be addressed to correct the jaundice.
Hepatic jaundice is caused by either primary or secondary liver disease. The liver cannot metabolize the normal levels of bilirubin, and so the levels rise until the tissues become saturated with the yellow pigment. Primary liver disease can be infectious, like leptosporosis and FIP, or functional, like liver cancer. Anorexic cats are prone to hepatic lipidosis, a condition where the liver swells with fat, leading to jaundice. Secondary liver diseases include hyperthyroidism and systemic fungal diseases. Anemia is usually not present in the case of hepatic jaundice.
Post-hepatic jaundice describes a condition where bile, the metabolized bilirubin, cannot pass from the liver through the bile duct and into the intestines where it is normally excreted from the body. This is called biliary stasis, and causes can include gall stones, pancreatitis, and tumors of the bile duct. In this case, the liver is capable of metabolizing the bilirubin; however, there is no place excrete it, and so it “overflows” into the blood-stream.
The prognosis for an animal with jaundice cannot be known without discovering the underlying disease that is causing this symptom. However, jaundice should never be ignored, since the disease process causing it can be potentially life-threatening.