Icterus in dogs and cats
By Dr. Garret Pachtinger, VMD, DACVECC
The presence of icterus (yellow discoloration of the skin and mucus membranes caused by excess bilirubin) is the strongest clinical evidence for the presence of hepatobiliary disease.
Icterus is caused by one of 3 major physiologic mechanisms:
Pre-hepatic icterus is caused by hemolysis of red blood cells, commonly seen in diseases processes including immune-mediated hemolytic anemia. Pre-hepatic icterus is easily diagnosed as the elevated bilirubin level is found concurrently with severe anemia in most cases. Hepatic icterus may be caused by any disease affecting the functional capacity of the liver. Post-hepatic icterus implies an extra-hepatic bile duct obstruction, with inability of the gall bladder to release bile (and the bilirubin contained within it) into the intestine.
While diagnosing pre-hepatic icterus (e.g., hemolyzed hematocrit tube) is often easy, differentiating hepatic from post-hepatic icterus can be more challenging. In both situations there will often be significant elevations of serum liver enzymes (ALT, AST, ALP, GGT). With that said, here are a few tips to help differentiate between hepatic and post-hepatic:
1. Hepatocellular leakage enzymes (ALT, AST) may be elevated to a more significant degree than cholestatic enzymes (ALP, GGT)
2. Other bloodwork findings may include signs of liver function impairment including decreased BUN, glucose, albumin and cholesterol
1. Cholestatic enzymes may be more significantly elevated
2. Serum cholesterol is often concurrently elevated
3. Physical examination may reveal pale or acholic feces
Ultimately additional testing such as an abdominal ultrasound may be needed, but we hope this helps with the initial evaluation and understanding of icterus in our small animal patients.