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Core Conditions - Abdominal > Interpretation of Liver Function Tests (LFTs) > Flashcards

Interpretation of Liver Function Tests (LFTs) Flashcards

1
Q

What are the 2 main reasons why LFTs are requested?

A
  • to confirm a clinical suspicion of potential liver injury or disease
  • to distinguish between hepatocellular injury (hepatic jaundice) and cholestasis (post-hepatic or obstructive jaundice)
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2
Q

What are the 7 components of a blood test used to assess liver function?

A
  • alanine transaminase (ALT)
  • aspartate aminotransferase (AST)
  • alkaline phosphatase (ALP)
  • gamma-glutamyltransferase (GGT)
  • bilirubin
  • albumin
  • prothrombin time (PT)
  • ALT, ASP, ALP and GGT are used to distinguish between hepatocellular damage and cholestasis
  • bilirubin, albumin and PT are used to assess the liver’s synthetic function
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3
Q

If ALT and/or ALP is raised, what do you have to decide about how much it is raised by?

A
  • if ALT is raised, decide if it is more than a 10-fold rise or less than a 10-fold rise
  • if ALP is raised, decide if it is more than a 3-fold rise or less than a 3-fold rise
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4
Q

What is ALT a useful indicator of and why?

A
  • ALT is found in high concentrations within hepatocytes
  • ALT enters the blood following hepatocellular injury
  • it is a useful marker of hepatocellular injury
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5
Q

What is ALP a useful clinical marker of and why?

A
  • ALP is concentrated in the liver, bile duct and bone tissues
  • it is often raised in liver pathology due to increased synthesis in response to cholestasis
  • ALP is a useful indirect marker of cholestasis
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6
Q

How is the rise in ALT and ALP compared to determine what type of problem is present?

A
  • a greater than 10-fold increase in ALT and a less than 3-fold increase in ALP suggests predominantly hepatocellular injury
  • a less than 10-fold increase in ALT and a greater than 3-fold increase in ALP suggests cholestasis
  • it is possible to have a mixed picture involving both hepatocellular injury and cholestasis
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7
Q

When is the level of gamma-glutamyl transferase reviewed and what may a raised GGT suggest?

A
  • the level of GGT needs to be reviewed if there is a rise in ALP
  • raised GGT can be suggestive of biliary epithelial damage and bile flow obstruction
  • it can also be raised in response to alcohol and drugs (e.g. phenytoin)
  • a markedly raised ALP with a raised GGT is highly suggestive of cholestasis
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8
Q

What would an isolated rise of ALP make you suspicious of?

A
  • a raised ALP in the absence of a raised GGT raises suspicion of n_on-hepatobiliary pathology_
  • ALP is also present in bone, so anything that leads to increased bone breakdown can elevate ALP
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9
Q

What are the 4 main causes of an isolated rise in ALP?

A
  • bony metastases or primary bone tumours (e.g. sarcoma)
  • vitamin D deficiency
  • recent bone fractures
  • renal osteodystrophy
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10
Q

What do blood tests typically show if a patient is jaundiced but ALP and ALT levels are normal?

A

an isolated rise in bilirubin is suggestive of a pre-hepatic cause of jaundice

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11
Q

What are the 2 causes of an isolated rise in bilirubin and what further investigations should be conducted?

A
  • the most common cause is Gilbert’s syndrome
  • haemolysis can cause an isolated rise in bilirubin
    • check a blood film, FBC, reticulocyte count, haptoglobin & LDH levels to confirm
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12
Q

What are the 4 main synthetic functions of the liver?

A
  • conjugation and elimination of bilirubin
  • synthesis of albumin
  • synthesis of clotting factors
  • gluconeogenesis
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13
Q

What 4 investigations can be used to assess the synthetic function of the liver?

A
  • serum bilirubin
  • serum albumin
  • prothrombin time (PT)
  • serum blood glucose
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14
Q

What is bilirubin and how does the liver process it?

A
  • bilirubin is a breakdown product of haemoglobin
  • the liver takes up unconjugated bilirubin and conjugates it
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15
Q

When does hyperbilirubinaemia cause clinically apparent jaundice?

A
  • hyperbilirubinaemia does not always cause clinically apparent jaundice
  • it is usually visible when bilirubin > 60 umol/L
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16
Q

What symptoms and signs that the patient has can distinguish whether there is conjugated or unconjugated hyperbilirubinaemia?

A
  • unconjugated bilirubin is NOT soluble in water

therefore, it does NOT affect the colour of the patient’s urine

  • conjugated bilirubin is water soluble and can pass into the urine as urobilinogen

this causes the urine to become darker in colour

17
Q

How can the colour of stools be used to differentiate the causes of jaundice?

A
  • if bile and pancreatic lipases cannot reach the bowel due to a blockage (e.g. in obstructive post-hepatic pathology)
  • this means that fat is not able to be absorbed
  • this results in stools that are more pale, bulky and difficult to flush
18
Q

How can the combination of the colour of urine and stools given an indication as to what type of jaundice might be present?

A
  • normal urine + normal stools = pre-hepatic cause
  • dark urine + normal stools = hepatic cause
  • dark urine + pale stools = post-hepatic (obstructive) cause
19
Q

What are the 3 most common causes of unconjugated hyperbilirubinaemia?

A
  • haemolysis (e.g. haemolytic anaemia)
  • impaired hepatic uptake (e.g. drugs, congestive cardiac failure)
  • impaired conjugation (e.g. Gilbert’s syndrome)
20
Q

What are the 2 most common causes of conjugated hyperbilirubinaemia?

A
  • hepatocellular injury
  • cholestasis
21
Q

What is the role of albumin?

A
  • it is synthesised in the liver
  • it helps to bind water, cations, fatty acids and bilirubin
  • it plays a role in maintaining the oncotic pressure of the blood
22
Q

For what 3 reasons might albumin levels fall?

A
  • liver disease resulting in decreased production of albumin (e.g. cirrhosis)
  • inflammation triggering an acute phase response which temporarily decreases the liver’s production of albumin
  • excessive loss of albumin due to protein-losing enteropathies
23
Q

What is prothrombin time (PT)?

A

it is a measure of the blood’s coagulation tendency, specifically assessing the extrinsic pathway

24
Q

What can an increased PT time indicate and why?

A
  • it can indicate liver disease and dysfunction in the absence of anticoagulant use and vitamin K deficiency
  • the liver is responsible for the synthesis of clotting factors
  • hepatic pathology impairing this process can result in increased PT time
25
Q

What does the AST / ALT ratio tell you about the functioning of someone’s liver?

A
  • the AST / ALT ratio is used to determine the likely cause of LFT derangement
  • ALT > AST is associated with chronic liver disease
  • AST > ALT is associated with cirrhosis and acute alcoholic hepatitis
26
Q

What is gluconeogenesis?

A

the metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substances

the liver plays a significant role in gluconeogenesis

27
Q

Why is serum blood glucose measured as part of an LFT?

A
  • the liver plays a significant role in gluconeogenesis
  • measuring serum blood glucose provides an indirect assessment of the liver’s synthetic function
  • gluconeogenesis tends to be one of the last functions to become impaired in the context of liver failure
28
Q

What would you expect ALT, ALP, GGT and bilirubin levels to be like in acute hepatocellular damage?

A
  • ALT is significantly raised
  • ALP is normal or slightly raised
  • GGT is normal or slightly raised
  • bilirubin is raised or significantly raised
29
Q

What would you expect the levels of ALT, ALP, GGT and bilirubin to be in chronic hepatocellular damage?

A
  • ALT is normal or slightly raised
  • ALP is normal or slightly raised
  • GGT is normal or slightly raised
  • bilirubin is normal or slightly raised
30
Q

What would you expect the levels of AST, ALP, GGT and bilirubin to be like in cholestasis?

A
  • ALT is normal or slightly raised
  • ALP is significantly raised
  • GGT is significantly raised
  • bilirubin is significantly raised
31
Q

What are the most common causes of acute hepatocellular injury?

A
  • poisoning (paracetamol overdose)
  • infection (hepatitis A or B)
  • liver ischaemia
32
Q

What are the 4 most common causes of chronic hepatocellular injury?

A
  • alcoholic fatty liver disease
  • non-alcoholic fatty liver disease
  • chronic infection (hepatitis B or C)
  • primary biliary cirrhosis
33
Q

What are the 3 less common causes of chronic hepatocellular injury?

A
  • alpha-1 antitrypsin deficiency
  • Wilson’s disease
  • haemochromatosis
34
Q
A

Core Conditions - Abdominal (13 decks)

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