liver function tests

what are the benefits of biochemistry liver function tests? (4)

- cheap
- easy
- good for monitoring
- if normal, can exclude liver diseases except in cirrhosis

what are the limitations of biochemsitry liver function tests? (5)

- not specific to the liver
- sensitivity varies with aetiology
- can only assess liver function over a long duration
- rarely definitive
- over-requested

what markers does a liver function test measure for? (9)

- albumin
- total bilirubin
- direct bilirubin
- prothrombin time (PT)
- AST
- ALT
- ALP
- gGT
- total protein

what do albumin results show?

liver function (protein synthesis)

why is albumin important?

maintains oncotic pressure of plasma, as it is a carrier protein

what does total protein results show?

liver function (protein synthesis)

what could an increase in total protein suggest?

increased immunoglobulins due to infection, inflammation etc.

what does prothrombin time (PT) results show?

activity of vitamin K-dependent clotting factors synsthesised by liver

what is prothrombin time (PT) recorded as?

International Normalised Ratio (INR)

what do total bilirubin and direct bilirubin results show?

cholestasis

when does jaundice usually appear in terms of bilirubin levels?

when bilirubin > 2x normal upper limit (34-51micromol/L)

what is direct bilirubin also known as?

conjugated bilirubin

what do ALT/AST results show?

hepatocellular injury

which out of ALT and AST is specific to the liver?

ALT

what happens to ALT when hepatocytes are injured?

enters blood

what do ALP/GGT results show?

cholestatic disease

where is ALT found in the liver?

hepatocyte cytoplasm

when does ALT increase?

- hepatocellular injury
- microsomal induction (e.g. drugs)

where is AST found in the liver?

hepatocyte mitochondria

where else is AST found? (4)

mitochondria of:
- cardiomyocytes
- renal cells
- myocytes
- brain cells

when does AST increase?

hepatocellular injury

what is the AST:ALT ratio in alcoholic liver disease?

>2

what could be the conditions if AST>ALT? (3)

- cirrhosis
- chronic hepatitis
- steatosis

what could be the condition if ALT>AST?

acute liver injury

where is ALP found?

biliary canaliculi

when does ALP increase?

cholestatic liver disease

why does ALP increase in cholestatic liver disease?

usually present in the bile, so obstruction to bile flow causes regurgitation of ALP into the blood

where is GGT found?

hepatocytes and biliary canaliculi

when is GGT raised?

hepatitis

what is total protein mainly used for?

screen for myeloma as it is raised in this condition due to 'paraproteins'

what is myeloma?

cancer of plasma cells made in bone marrow

what are albumin results used for mainly?

hypoalbuminaemia - which could be caused by liver disease

what could decrease the level of albumin in the liver? (5)

- decreased synthesis
- haemodilution
- altered distribution
- increased loss of albumin
- increase catabolism

what could cause decreased synthesis of albumin? (2)

- severe liver disease
- malnutrition

what could cause haemodilution of albumin? (4)

- pregnancy
- IV infusion
- congestive heart failure
- cirrhosis

what could cause altered distribution of albumin? (4)

- injury
- infection
- inflammation
- malignancy

what could cause increased loss of albumin? (3)

- skin (burns)
- gut
- renal

what could cause increased catabolism of albumin? (2)

- acute/chronic illness
- malignancy

what are the 3 biochemical types of liver disease?

- hepatic
- cholestatic
- mixed pattern

what are the levels of enzymes in hepatic liver disease? (4)

- increase ALT
- increase AST
- increase GGT
- no change ALP

what are the levels of enzymes and bilirubin in cholestatic hepatobiliary disease? (5)

- increased ALP
- increased GGT
- increased/normal bilirubin
- increased/normal ALT
- increased/normal AST

what should we be weary of when testing for ALP?

it can be raised in other conditions e.g. bone disease + metastasis

what should you check ALP alongside with to check for actual liver abnormalities?

GGT

what immunglobulins can you test for specific liver diseases?

IgA - alcoholic liver disease
IgG - autoimmune hepatitis
IgM - primary biliary cirrhosis

how is ammonia linked with the liver?

converted to urea

what happens to the ammonia in abnormal liver function?

- does not get converted to urea and excreted
- can cross blood-brain barrier and exert neurotoxic effects
- leading to encephalopathy

what are other methods of investigation for liver disease?

- ultrasound
- CT/MRI scan
- liver biopsy
- magnestic resonsce cholangiopancreatography (MRCP)
- markers/scores of fibrosis
- fibroscan (check for liver elastopgraphy)

what could an ultrasound show?

- fatty liver
- jaundice
- gallstones
- lesions > 1cm

what would a CT/MRI scan show?

tumours

what would a magnetic resonance cholangiopancretogrpahy (MRCP) show?

biliary system

how would you investigate non-alcoholic fatty liver disease (NAFLD)? (2)

- ultrasound
- rule out other suspisions from the history and NOT LFTs

common risk factors for non-alcoholic fatty liver disease?

- obesity
- type II diabetes mellitus

what is the best marker of liver synthetic function?

prothrombin time