Liver Function Tests Flashcards
What are the 8 liver functions tests that can be ordered?
Must order 6 or more of the following tests:
- Protein
- Albumin
- Plasma Bilirubin - unconjugated and conjugation
- Plasma transferases: ALT (alanine aminotransferase) and AST (aspartate aminotransferase)
- Plasma alkaline phosphatase (ALP)
- Gamma-glutamyl transferase (GGT)
- LD (lactate dehydrogenase)
What is the difference between conjugated and unconjugated bilirubin?
Unconjugated - from RBCs b’down
Conjugated - after metabolism in the liver
Where are the different enzymes located in a hepatocyte?
Cytoplasm: ALT, AST, LD
Membrane: ALP, GGT
Mitochondria: AST
What enzymes are associated with hepatocellular damage?
ALT, AST, LD (cytoplasmic)
Cause: virus, toxin (NSAIDs), anoxia
NB: AST is especially related to toxins
What enzymes are associated with biliary disease?
ALP, GGT (biliary membrane)
Cause: gallstones, cancer of biliary tree (inc gallbladder, tree, pancreas)
What increases enzymes in the cell (enzyme induction)?
Alcohol and anticonvulsants
increase GGT and ALP in the cell
ALT:
- Function
- Location
- Half life (how long does it stay in the blood)
Function: ALT (alanine transaminase) is the enzyme part of gluconeogenesis
Location:
*only cytoplasmic
*liver»_space;»> muscle, kidney
therefore considered ‘L’iver specific
Half life: 36 hours
= indicator of hepatocellular damage
= specific to liver
= raised in obesity, fatty liver, metabolic syndrome
AST
- Function
- Location
- Half life (how long does it stay in the blood)
Function: AST is an enzyme that is a part of the Kreb’s cycle
Location
- both cytoplasmic and mitochondrial
- liver, muscle, blood cells (as needed in mitochondria)
Half life: 18 hours
= indicator of hepatocellular damage
AST
- Function
- Location
- Half life (how long does it stay in the blood)
Function: AST is an enzyme that is a part of the Kreb’s cycle
Location
- both cytoplasmic and mitochondrial
- liver, muscle, blood cells (as needed in mitochondria)
Half life: 18 hours
What does AST > ALT indicate?
- Indicates that it is acute and affects the mitochondria
- Usually EtOH, toxin
What does ALT > AST indicate?
- Indicates that it is chronic (not as severe), resolving
- Usually hepatitis (still can be drugs, viral, metabolic e.g. hypoxia)
Why is the half life of ALT and AST important?
ALT half life 36 hrs; AST half life 18 hrs
In early stages, more AST is released (as baseline concentration is higher). Therefore in first 18hr - AST > ALT (acute indicator)
In later stages ( >18h), ALT has the longer half life therefore appears higher than AST (chronic indicator)
i.e. in chronic diseases, AST can seem normal, but ALT elevated
What are the common viral diseases that affect the liver (hepatitis)?
Acute: HAV, HEV - presents with high levels of ALT
Chronic: HBV (and HDV), HCV - presents with low levels of ALT
Other that cause hepatitis: EBV CMV Q Fever Rubella
What are the common drugs and toxins that cause hepatocyte damage?
Basically any drug can but most common are: - ABx: flucloxacillin, amoxil Statins: atorvastatin, simvistatin, etc - Ethanol - Paracetamol - Herbal tea (kombucha)
What are the common drugs and toxins that cause hepatocyte damage?
Basically any drug can but most common are: - ABx: flucloxacillin, amoxil Statins: atorvastatin, simvistatin, etc - Ethanol - Paracetamol - Herbal tea (kombucha)
Can a pt have liver damage with normal ALT but AST elevated?
No - if AST is elevated independent of ALT, it is indicating that it is coming from somewhere else in the body. ALT that is the cytoplasm must increase if the mitochondria is being damaged
e.g. Simvistatin - although it causes liver damage, it also causes muscle damage
If a pt has slightly elevated ALT, but normal AST what can this indicate?
Chronic or resolving hepatitis
Why can a cirrhotic liver present with normal LFTs?
The liver has been so damaged, it has nothing else to produce and release
ALP:
- Location
- Function
Location: bone (40%), liver (60%), placenta (consider this if F pregnant)
- it is present on the sinusoidal surface of hepatocytes and bile canaliculi and ducts
Function: it is not specific to liver but an indicator of cholestasis (obstruction, infiltration, cirrhosis)
GGT:
- Function
- Location
Function: gamma glutamyl transferase in amino acid transport (to produce glutathione)
Location: liver, biliary epithelium, renal
- present in bile cannaliculi
- raised level of cholestasis, other liver disease and drug and alcohol intake
Liver enzyme profile of fatty liver
Increase ALT (as it is a chronic disease)
