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Biochemistry > Liver Function Tests > Flashcards

Liver Function Tests Flashcards

1
Q

alanine aminotransferase (ALT) is found

A

hepatocyte cytoplasm, some in muscle

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2
Q

aspartate transaminase (AST) is found

A

in hepatocyte cytoplasm and mitochondria

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3
Q

lactate dehydrogenase is found

A

in the cytoplasm; high concentrations in muscle and liver

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4
Q

alkaline phosphatase (ALP) is found

A

on the canalicular surface of hepatocytes and bone during formation

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5
Q

gammaglutamyl transpeptidase (GGT) is found

A

canalicular surface of hepatocytes

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6
Q

Liver necrosis releases which enzymes?

A
  • AST (+toxins), ALT, LD
  • due to virus, toxins, anoxia, paracetamol
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7
Q

In biliary disease causing obstruction, what liver enzymes are released?

A

ALP & GGT (via lymphatics)

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8
Q

Which liver enzymes are released in response to drugs (including alcohol)?

A
  • not in response to damage
  • increased production of ALT and GGT in response to alcohol, anticonvulsants
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9
Q

Which enzyme is most liver specific?

A

ALT

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10
Q

ALT catalyzes

A

pyruvate <–> alanine

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11
Q

AST is involved in

A
  • aspartate –> glutamate
  • oxaloacetate and malate movement in/out of mitochondria
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12
Q

Release of AST suggests

A

damage to cytosol and mitochondria of any cell containing them (liver, muscle, blood)

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13
Q

Elevated ALT suggests

A

cytosolic damage, most likely in liver (less so in muscle, kidney)

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14
Q

AST is removed

A

by the kidney, 2x as fast as ALT (18hrs)

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15
Q

ALT is removed

A

by the liver, slower than AST (36hrs)

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16
Q

If AST > ALT

A
  • acute injury affecting cytoplasm and mitochondria
  • eg alcohol, toxins
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17
Q

If ALT > AST

A
  • chronic or resolving injury
  • AST has gone away but the ALT is accumulating
  • eg hepatitis
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18
Q

ALT levels in Hep A

A
  • mild = 250
  • moderate = 1000
  • severe = 5000
  • ALT > 10 000 = death
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19
Q

Normal ALT is

A

<50 IU/L

20
Q

ALT in acute Hep B infection is

A

~2000-5000

(core positive IgM, current infection)

21
Q

ALT in chronic Hep B infection is

A

much lower than acute, ~50-250

(SA Ag positive, chronic infection)

22
Q

ALT levels in chronic hepatitis infections

A

are typically lower than in acute

23
Q

What types of drugs can cause hepatic damage?

A
  • antibiotics
  • statins
  • ethanol
  • paracetamol
  • herbal tea/kombucha
24
Q

AST and ALT > 10x normal suggest

A

acute or severe insult:

drugs, acute viral hepatitis, CMV (glandular fever), hypoxia, splenomegaly

25
Q

ALT and AST > 5x normal suggests

A

infection, alcohol, fatty liver disease, medications

26
Q

Elevated AST without elevation in ALT suggests

A

muscle and/or red cell damage eg statins causing muscle wasting

(ie mitochondrial damage in tissues other than liver)

27
Q

Creatine kinase levels can be estimated by

A

AST x 20

normally <200

28
Q

ALT elevated without an elevation in AST suggests

A

chronic or resolving disease eg Hep B, Hep C

29
Q

What happens to ALT and AST levels as the liver approaches cirrhosis?

A

they decrease; there are fewer hepatocytes left to damage and release ALT and AST

30
Q

Total protein is normally

A

60-80g/L

31
Q

normal albumin is

A

35-55g/L

32
Q

normal ALP is

A

<120 IU/L

33
Q

normal bilirubin is

A

<26mmol/L

34
Q

normal GGT is

A

<50 IU/L

35
Q

normal AST is

A

<45 IU/L

36
Q

Raised ALP is normal in

A

3rd trimester of pregnancy; produced by placenta

37
Q

Increased GGT suggests

A

biliary disease

38
Q

What is the function of GGT?

A
  • transfers glutamyl groups to AA
  • helps transport of AA across membranes
  • important in production of glutathione
39
Q

What is the function of ALP?

A
  • adds phosphate groups to things in membranes in alkaline environments
40
Q

In extra-hepatic biliary obstruction (cancer, stones), GGT and ALP

A

increase significantly, up to 20-30x normal levels

41
Q

In intra-hepatic biliary obstruction, GGT and ALP

A

will be mildly elevated, bilirubin should be normal

can be due to tumours affecting small parts of liver or induction by drugs etc.

42
Q

Intrahepatic biliary obstruction can be due to

A

damage to a small part of the tree (tumour, lesion, etc.(

or drugs inducing enzymes (alcohol, convulsants)

43
Q

What is the commonest cause of liver enzyme elevation?

A

obesity

44
Q

Which enzyme does BMI affect?

A

ALT; AST less-so because it can disappear, GGT affected more in the intermediate/pre-diabetic stage of obesity

45
Q

What causes fatty liver in obesity?

A
  • fructose
    • from high fructose corn syrup
    • from sucrose (fructose + glucose)
46
Q

How does fructose cause fatty liver in obesity?

A
  • only body tissue it can enter is liver
  • liver can convert fructose into glucose but not likely to do so because dietary glucose is sufficient
    • insulin response tells liver not to make glucose from fructose bc sugar is abundant in blood
  • fructose instead gets broken down into 3C units that are turned into fat

Biochemistry (5 decks)

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