19: Liver Function

Definition of liver failure

Failure to synthesize or failure to clear products

Icterus

Increased bilirubin

Source of bilirubin

Heme breakdown

Immediate breakdown product of heme

Unconjugated bilirubin

How does unconjugated bilirubin get to the liver

Via blood on a carrier protein

Clinicopathologic changes seen with extravascular hemolysis

Hyperbilirubinemia and hyperbilirubinuria

Clinicopathologic changes seen with intravascular hemolysis

Hemoglobinemia and hemoglobinuria

How are RBCs broken down

By macrophages in the spleen

How is unconjugated bilirubin kept inside hepatocytes

Binds to ligandin

Once bilirubin is conjugated, how does it exit the liver

Through the bile canaliculus

Cause of pre-hepatic hyperbilirubinemia

Increased RBC destruction that overwhelms healthy liver capacity

Cause of hepatic hyperbilirubinemia

Not enough healthy hepatocytes to handle the normal amount of unconjugated bilirubin coming in

Clinicopathologic changes that will accompany hepatic hyperbilirubinemia

Decreases in other liver products: TP/alb, BUN, cholesterol, glucose

Cause of post-hepatic hyperbilirubinemia

Liver can’t excrete the bile produced

Species that has a fasting hyperbilirubinemia

Horses

Bilirubin present in bilirubinuria

Conjugated bilirubin → not bound to a protein!

Species that may normally have bilirubin in concentrated urine

Dogs

Cause of increased bilirubin in ruminants

Think hemolysis, it is not consistently increased with liver disease

Bile acid function

Aids in digestion and absorption of fat and fat soluble nutrients

Source of bile acids

Cholesterol

Where are bile acids stored

Gall bladder

Proper way to conduct a bile acid test

Take a pre and post prandial sample

Species that doesn’t need two samples for a bile acids test

Horses (or anything without a gall bladder)

Causes of increased bile acids

• Portosystemic shunts

• Decreased functional hepatic mass (liver failure)

• Cholestasis

Indications for bile acid testing in horses

Can differentiate between a fasting hyperbilirubinemia and a hepatic/post hepatic hyperbilirubinemia

Result of bile acids in a horse with fasting hyperbilirubinemia

Normal bile acids

Result of bile acids in a horse with a hepatic/post-hepatic hyperbilirubinemia

Increased (?) bile acids

Why is it pointless to test liver function via bile acids in a patient with cholestasis

The bile acids will be elevated due to the cholestasis anyways, the blockage needs to be resolved before you test liver function with bile acids

Liver function/hyperbilirubinemia test that is not altered by cholestasis

Blood ammonia

Parameters that are used to evaluate liver function

• Albumin

• BUN

• Glucose

• Cholesterol

Why does severe cholestasis cause problems with PT/PTT

Low vitamin K absorption → looks like vit K antagonism → bleeding disorder