Clinical pathology

Question 1

What is measured to assess liver damage?

Answer 1

Hepatocellular and induced biliary enzymes

Question 2

What is measured to assess liver function?

Answer 2

Bilirubin and bile acids

Question 3

What are the 4 hepatocellular enzymes measured to assess liver damage?

Answer 3

Alanine aminotransferase (ALT) Aspartate aminotransferase (AST) Sorbitol dehydrogenase (SDH) Glutamate dehydrogenase (GLDH)

Question 4

Describe the properties of ALT

Answer 4

• Found in cytosol - Liver specific - Increased ALT due to degenerative change of hepatocytes - Only used in small animals - Increase in circulation, proportional to hepatic mass effected - Poor correlation between serum levels and hepatic dysfunction

Question 5

Describe the properties of AST

Answer 5

• Isoenzyme - Found in cytosol, mitochondria, RBC, skeletal and cardiac muscle

Question 6

What else could elevated levels of AST suggest?

Answer 6

Haemolysis or muscle injury

Question 7

Describe the properties of SDH

Answer 7

• Found in cytosol - Useful in horses and cattle - Degrades v quickly once blood sample is taken *not many labs offer this*

Question 8

Describe the properties of GLDH

Answer 8

• Found in cytosol - Sensitive marker for hepatic injury - Useful in horses and cattle

Question 9

What are the 2 biliary enzymes that can be measured to assess liver damage?

Answer 9

Alkaline phosphatase (ALP) Gamma glutamyl transferase (GGT)

Question 10

Describe the properties of ALP

Answer 10

• Found in hepatocytes in biliary epithelium
• Cholestasis markedly increases ALP activity
• Damage to liver parenchyma induces ALP, increases serum levels
• Increased levels can indicate cholestasis, drug induction (dogs), bone remodelling

Question 11

Draw a diagram to demonstrate the production of ALP

Answer 11

Question 12

ALP and cats…

Answer 12

• Produce lot less ALP
• Has much shorter half life
• Steroids don’t induce it
• Elevation is significant
• Indicator of feline hyperthyroidism

Question 13

Describe the properties of GGT

Answer 13

• Membrane bound enzyme found in hepatobiliary system and renal tubules
• Useful in cttle, horses, cats
• Elevated levels may indicate cholestasis
• In renal disease found in urine

Question 14

How can hyperbilirubinaemia be classified?

Answer 14

Pre-hepatic, hepatic, post-hepatic

Question 15

What are the features of pre-hepatic hyperbilirubinaemia?

Answer 15

1. Haemolysis occurs causing Hb to degrade to bilirubin
2. Circulating [bilirubin] increases
3. Liver overwhelmed
4. Conjugation with albumin occurs in liver as normal but not at a fast enough rate

Question 16

What are the features of hepatic hyperbilirubinaemia?

Answer 16

Bilirubin levels increase due to a decreased liver functional mass, i.e. reduction in healthy hepatocytes

Question 17

What are the causes of post-hepatic hyperbilirubinaemia?

Answer 17

• Obstructive cholestasis (intra/extra hepatic obstruction of bile flow; ability to uptake bilirubin inhibited)
• Functional cholestasis (infection in ducts, affects peristalsis)

Question 18

Draw a diagram to explain normal bile acid metabolism

Answer 18

Question 19

Using a diagram explain what happens to bile metabolism with a portosystemic shunt

Answer 19

Question 20

Using a diagram explain what happens to bile metabolism when there is a reduced hepatic functional mass

Answer 20

Question 21

Using a diagram explain what happens to bile metabolism during cholestasis

Answer 21

Question 22

How would you test bile acid levels?

Answer 22

Cats and dogs:

• Fast animal, take a sample then take another 2 hrs post-prandial
• Normal, level should be low in both samples
• Abnormal, increased levels in 2nd sample

Horses:

• Single measurement used as have no gall bladder