GI jaundice & LFTs

Question 1

What is jaundice?

Answer 1

Clinical manifestation of raised bilirubin

Yellow skin and iris

Question 2

How is bilirubin formed?

Answer 2

Splenic macrophages engulf and digest erythrocytes in

spleen: Hb -> haem (+ globin) -> bilirubin (unconjugated/ albumin bound) -> blood ->
liver: conjugation -> bilirubin (conjugated/ water soluble) ->

3 options: 1. enterohepatic circulation (kidney/ gut/ liver) 2. go to kidney -> urobilinogen-> urine excreted 3. Move to gut-> urobilinogen-> sterocobilin (oxidised) excreted faeces

Question 3

What causes pre-hepatic jaundice? What is the main problem if this occurs in infants?

Answer 3

Too much haem
(Increased degradation of Hb) -> too much demand on liver so raised unconjugated bilirubin

E.g. sickle cell anaemia, thalassaemia, spherocytosis -> damage to RBC -> haemolysis

In newborns bilirubin can cross the blood brain barrier -> neurological damage

Question 4

What causes hepatic jaundice?

Answer 4

Reduced conjugating ability of liver from damage to hepatocytes, can get a mixture of conjugated and unconjugated if parts of liver working e.g.

Wilson’s disease, meds, hereditary haemochromatosis, alcoholism, drugs, auto-immune, viral hepatitis, infections, deposition disorders, fatty liver disease, NAFLD

Acute liver damage: paracetamol toxicity, acute viral hepatitis, other infections

Question 5

What causes post-hepatic jaundice?

Answer 5

Obstruction to the excretion pathway, raised conjugated bilirubin (water soluble so more excreted by kidneys -> dark urine & pale stools

E.g. gallstones, biliary stricture,
pathology to the head of pancreas (pancreatic cancer)

Question 6

When might hepatic and pre-hepatic jaundice occur simultaneously?

Answer 6

Intrahepatic pathology (oedema, growth, scarring) can compress intrahepatic bile ducts so can’t enter liver

Question 7

What do liver functions tests look for? Why is calling them ‘function tests ‘ not very accurate?

Answer 7

Bilirubin C&UC And albumin (& other synthesised proteins) test the function of the liver but

Alanine transaminase, aspartate aminotransferase, alkaline phosphatase increases when there is damage to hepatocytes so don’t really test function

Question 8

When does ALT and AST increase?

Answer 8

ALT alanine transaminase (more specific to the liver) rises more than AST in acute liver damage

AST aspartate transaminase (also found in cardiac/ skeletal muscle and RBCs) rises more than ALT in cirrhosis and alcoholic hepatitis

Question 9

When does ALP increase.?

Answer 9

Alkaline phosphatase

Found in cells lining the bile duct, increases in cholestasis (bile duct obstruction)

But also increases in bone growth of children

Can use gamma- glutamyl transferase (Gamma GT) to specify source as liver
⬆️ALP ⬇️GGT = bone growth
⬆️ALP⬆️GGT = bile duct problem

Question 10

What can LFTs show?

Answer 10

LFT abnormalities help identify the cause of jaundice (can be abnormal without jaundice too), give a pattern or picture: hepatocellular damage, obstructive (cholestasis) or mixed