Liver Tests

Question 1

What are the main patterns (clinical and laboratory) of liver damage?

How does each present?

Answer 1

Hepatocellular:

• injury to hepatocytes
• elevated AST/ALT

Cholestatic:

• injury to bile ducts
• elevated bilirubin
• elevated alk phos/GGT
• jaundice + pruritis

Question 2

What labs are the main labs associated with the liver?

Answer 2

• bilirubin
• AST/ALT
• alkaline phosphatase
• γ-glutamyl transpeptidase (GGT)
• INR (coagulation factors)

PT (coagulation factors)

• albumin
• ammonia

Question 3

What labs are associated with hepatocellular damage?

Answer 3

-transaminases (AST/ALT)

Question 4

How are AST/ALT used to assess the liver?

Answer 4

They are located in the the cytoplasm (and mitochondria for AST) of hepatocytes and are released with injury

some degree of elevation will be noted in all form of liver injury

• most elevated in acute conditions; necrosis, toxic injury, and acute viral hepatitis (>3000)
• less elevated in chronic conditions; chronic viral hepatitis, alcoholic liver disease, NAFLD (100-300)

Question 5

What is the sensitivity/specificity of AST/ALT?

Answer 5

both are sensitive for liver damage

• ALT is more specific
• AST is less specifi

Question 6

What labs are associated with cholestasis?

Answer 6

• alkaline phosphatase
• GGT
• bilirubin

Question 7

How are alkaline phosphatase and GGT used to assess the liver?

What is the sensitivity/specificity?

Answer 7

both are sensitive to cholestasis/damage to biliary tract

• alkaline phosphatase is less specific (can be seen in bone disorders and other tissues)
• GGT is specific to liver

elevated alk phos w/ GGT = liver

elevated alk phos w/o GGT = non-liver

Question 8

What is uncongjugated bilirubinemia suggestive of?

Answer 8

Unconjugated:

• increased production of bilirubin; exceeds livers capability to clear (pre-hepatic)
  
  • hemolysis
  • reabsorption of hemorrhage
• hepatic uptake of bilirubin (intrahepatic)
  
  • drug interference with uptake
• metabolism; ability to conjugate (intrahepatic)
  
  • UGT1A1 (function/expression); Gilbert and Crigler-Najjar syndromes
  • liver diseases through physiologic stress

Question 9

What is congjugated bilirubinemia suggestive of?

Answer 9

Conjugated:

• transport of bilirubin into canaliculi (intrahepatic)
  
  • Dubin-Johnson/Rotor syndromes
• intrahepatic obstruction
  
  • liver diseases through inflammation and swelling of the liver
  • primary biliary cholangitis; autoimmune
• extrahepatic obstruction
  
  • choledocholithiasis
  • tumor compressing biliary tree
  • primary biliary cholangitis and primary sclerosing cholangitis
  • infection

Question 10

What labs are associated with liver function?

Answer 10

• PT/INR
• albumin
• ammonia
• cholesterol

Question 11

What is mixed bilirubinemia suggestive of?

Answer 11

Mixed:

• viral hepatitis
• alcohol-related liver disease (can also be conjugated predominant)

Question 12

What test is most useful for assessing acute changes in liver function?

Chronic changes?

Answer 12

PT/INR; assess factor VII which has the shortest half-life of the coagulation factors so PT/INR will show the earliest change

albumin has a long half-life and is therefore more useful in assessing chronic changes as it is less likley to show transient fluctuations