Liver Function Test Flashcards
Why is a liver function test performed?
- To confirm a clinical suspicion of liver injury or disease
- To distinguish between hepatocellular injury (hepatic jaundice) and cholestasis (post-hepatic or obstructive jaundice)
What are the liver function test reference ranges?
ALT 3-40 iu/l AST 3-30 iu/l ALP 3-100 umol/l GGT 8-60 u/l Bilirubin 3-17 umol/l Albumin 35-50 g/l PT 10-14 seconds
What is alanine transaminase (ALT) ?
A marker of hepatocellular injury.
Found in high concentration within hepatocytes and enters the blood following hepatocellular injury
What is Alkaline Phosphatase ?
A protein that is concentrated in the liver, bile duct and bone tissues.
Is raised in liver pathology due to increased synthesis in response to cholestasis
What does a >10 fold increase in ALT and < 3 fold increase in ALP indicate?
Hepatocellular injury
What does a < 10 fold increase in ALT and a > 3 fold increase in ALP indicate?
Cholestasis
When should Gamma GT be reviewed?
When there is a rise in ALP
What does an increase in Gamma GT indicate?
Biliary epithelial damage and bile flow obstruction.
Can also be raised in response to alcohol and drugs
What does a markedly raised ALP and GGT indicate?
Cholestasis
What does an isolated ALP increase indicate?
non-hepatobiliary pathology. Bone breakdown will raise ALP levels:
- bony metastasis or primary bone tumours
- vitamin D deficiency
- recent bone fractures
- renal osteodystrophy
What does an isolated rise in bilirubin indicate?
Pre-hepatic jaundice, usually caused by Gilbert’s syndrome or haemolysis
What should be done if haemolysis is suspected?
Check blood film, FBC, reticulocyte count, haptoglobin and LDH
Name some of the liver’s synthetic functions?
Conjugation and elimination of bilirubin
Synthesis of albumin
Synthesis of clotting factors
Gluconeogenesis
What investigations assess synthetic liver function?
Serum bilirubin
Serum albumin
Prothrombin time
Serum blood glucose
What is bilirubin?
A breakdown product of haemoglobin
Where is bilirubin conjugated?
The liver
How does conjugated hyperbilirubinaemia affect urine?
It is water soluble so will pass into urine as urobilinogen = darker urine
How does unconjugated hyperbilirubinaemia affect urine?
It is not water soluble so will not affect the colour of urine
When may stools be able to differentiate between the causes of jaundice?
Can determine if jaundice is post-hepatic jaundice as blockage = bile and pancreatic lipase unable to reach bowel = steatorrhoea
Normal urine + normal stools
Pre-hepatic cause of jaundice
Dark urine + normal stools
Hepatic cause of jaundice
Dark urine + pale stools
Post hepatic cause
Name some causes of unconjugated hyperbilirubinaemia?
Haemolysis (haemolytic anaemia)
Impaired hepatic uptake (drugs, congestive heart failure)
Impaired conjugation (gilbert’s syndrome)
Name some causes of conjugated hyperbilirubinaemia ?
Hepatocellular injury
Cholestasis
Rotor’s syndrome
Dubin-Johnson Syndrome
What is the function of albumin?
Synthesised in the liver and helps to bind water, cations, fatty ions and bilirubin. It also plays a key role in maintaining oncotic pressure of blood.
Why might albumin levels fall?
Liver disease = decreased production of albumin
Inflammation triggering an acute phase response which temporarily decreases albumin production
Excessive loss of albumin due to protein-losing enteropathies or nephrotic syndrome
What is prothrombin time?
A measure of the bloods coagulation tendency. Assesses the extrinsic pathways
Name some secondary causes that may increase PT?
Anticoagulants and Vit K deficiency
Why can PT be increased in hepatic pathology?
Because the liver is responsible for clotting factor synthesis
What happens when ALT>AST ?
Chronic liver disease
What happens when AST>ALT?
Cirrhosis
Acute alcoholic hepatitis
What are the causes of acute hepatocellular injury?
Poisoning (paracetamol overdose)
Infection (hep A and B)
Liver ischaemia
Causes of chronic hepatocellular injury?
Alcoholic fatty liver disease
NAFLD
Chronic infection (hep B or C)
Primary billiary cirrhosis
What are some uncommon causes of chronic hepatocellular injury?
Alpha-1 antitrypsin deficiency
Wilson’s disease
Haemochromatosis
