Use of Liver Enzymes in Diagnosis Flashcards
Which liver enzymes are cytoplasmic?
ALT, AST and LD
Which liver enzymes are on the cell membrane?
ALP and GGT
Which liver enzymes are in organelles?
mitochondrial AST and lysosomal SOD
Which liver enzymes will be increased in the plasma due to necrosis of hepatocytes?
ALT, AST and LD
Which liver enzymes will be increased in the plasma due to biliary disease (where the membrane is distressed)?
ALP and GGT
What is the action of ALT?
converts pyruvate to alanine in the Cori cycle
What is the action of LD?
converts lactate to pyruvate in the Cori cycle
What is the action of AST?
converts aspartate to glutamate
Is there more AST or ALT in a hepatocyte?
AST because it is in the cytosol and in the mitochondria
What is the key difference between AST and ALT?
ALT is specific to hepatocytes but AST is not
Which lasts longer in the blood - AST or ALT?
ALT
Which is higher in an acute disease and which is higher in a chronic disease of AST and ALT?
AST is higher in acute, ALT is higher in chronic
What is the level of ALT in hepatitis A?
250 if mild, 1000 if moderate, 5000 if severe
How can you distinguish between acute and chronic hepatitis B?
the ALT level - very high (5000) if acute and lower (250) if chronic
What are some drugs which cause liver disease?
flucloxacillin, amoxil, statins, ethanol, paracetamol
If AST is the only liver enzyme which is high is it liver disease?
No - must have AST and ALT together if liver disease
Are AST and ALT always high in cirrhosis?
No - if cirrhosis is so end stage that there are no hepatocyte left to release AST and ALT then the levels could be normal - this is a very bad sign
Where else is ALP apart from the liver?
bone - good marker of bone disease - also produced in the placenta in pregnancy
What is the action of GGT?
transfers glutamyl groups to amino acids - important in production of glutathione
What is the action of ALP?
adds phosphate groups
What are the liver enzymes like in an extra hepatic biliary obstruction?
huge elevation of GGT and ALP
What are the liver enzymes like in an intra hepatic biliary obstruction?
milder elevation of GGT and ALP
Is there a correlation between GGT level and amount of alcohol consumed?
no
Why is GGT elevated in alcoholic liver disease?
ethanol leads to depletion of NAD+ which causes an up regulation of GGT to make glutathione
What is another cause of GGT elevation?
anti-epileptic drugs
Why is there never an absolute picture of hepatocellular death or biliary obstruction?
because biliary obstruction causes hepatocellular death and hepatocellular death causes biliary obstruction
What is the commonest cause of liver enzyme elevation?
obesity
Do liver function tests indicate liver function?
no - they are markers of liver damage
