Liver Function Tests (LFTs) Flashcards
What are the functions of the liver?
produces and excretes bile required for food digestion (fat)
carbohydrate metabolism: gluconeogenesis, glycogenolysis and glycogenesis
breakdown of insulin and other hormones
- e.g. testosterone and oestrogens
lipid metabolism: cholesterol synthesis and the production of triglycerides (fats)
produces coagulation factors and plasma proteins
- e.g. albumin
breaks down haemoglobin (bile pigments are its metabolites), toxic substances and most medicinal products
converts ammonia to urea
stores a multitude of substances
- glucose as glycogen, fat soluble vitamins, vitamin B12, iron and copper
main site of red blood cell production in the first trimester foetus
What are the different tests that can be done in liver function tests?
serum specimens looking at
- bilirubin
- aminotransferases
= alanine amino transferase (ALT) and aspartate aminotransferase (AST)
- alkaline phosphate (ALP)
- gamma glutamyl transferase (GGT)
- albumin
- prothrombin time
What is bilirubin? How is it formed? How’s transported around the body and excreted?
bilirubin (yellow pigment) is a metabolite of haemoglobin breakdown
- broken down in the liver, spleen and bone marrow
unconjugated bilirubin is transported via protein binding
- is bound to albumin
bilirubin is conjugated in the liver
- leaves via the bile duct, enters the gut and is excreted via stools as stercobilinogen
What is the normal range of bilirubin? What are high levels of bilirubin caused by?
normal range is <17 micromol/litre
high blood bilirubin is caused by:
- haemolysis
- failure of the conjugating mechanism within the hepatocytes due to hepatocellular damage caused by infection
= viral hepatitis or by toxin (paracetamol overdose)
- obstruction in the biliary system, cholestasis caused by gall stones
- gilbert syndrome = genetic condition affecting the enzyme needed to conjugate bilirubin
What is jaundice? What are the symptoms? At what level of bilirubin does it occur?
occurs at bilirubin levels >50 micromol/litre
jaundice is a condition that causes the skin and whites of eyes to turn yellow
- itching
= can be treated using antihistamines, skin emollients or cholestyramine (binds to bilirubin to excrete it)
What is cholestasis? What are the symptoms associated? Who is it dangerous in? What can be used to treat it?
cholestasis
- blocked or slowed bile flow
results in intense itching
- can be treated using antihistamines, skin emollients or cholestyramine (binds to bilirubin to excrete it)
is dangerous in pregnant women
- should be referred to their GP/hospital
What are the different aminotransferases? What are their normal ranges? Where are they found?
alanine aminotranferase (ALT)
- 5-40 U/L
- is found mainly in the liver
= are not membrane associated (found in the cytosol)
aspartate aminotransferase (AST)
- 10-40 U/L
- is found in various tissues = heart, skeletal muscle, kidney, brain, liver
What do high levels of AST and ALT indicate?
high enzyme levels indicate acute kidney damage
- are the fastest indicator
small increases are seen in obstructive jaundice and cirrhosis
an AST:ALT ratio of more than 2:1 is characteristic in patients with alcoholic liver disease
- alcohol causes vitamin B deficiency, vitamin B6 is responsible for AST and ALT synthesis
= ALT is more dependent so would be lower
What is the normal range of alkaline phosphate? What do abnormal levels indicate?
ALP
- normal range is 30-300 U/L
is the main indicator for cholestasis
high levels occur in the presence of tumours and cirrhosis
circulating ALP can be derived from bone
- raised serum levels are found in Paget’s disease, osteomalacia
= if only ALP is raised then the issue may be related to bone health
How can cholestasis and acute hepatic damage be differentiated?
high gamma glutamyl transpeptidase (GGT) and alkaline phosphate (ALP)
- cholestasis
high gamma glutamyl transferase (GGT) and AST/ALT ratio > 2
- acute hepatic damage
What is gamma glutamyl transpeptidase? What is its normal range? What does high levels indicate?
GGT normal range is
- M < 50 U/L, F < 32 U/L
GGT is a microsomal enzyme widely distributed in tissues
high GGT with no other LFT abnormalities
- caused by alcohol or enzyme inducing drugs
high GGT with high ALP
- cholestasis
high GGT with AST/ALT > 2
- acute hepatic damage
What is albumin? What is the normal range? What do low and high levels indicated/cause?
albumin is a protein made by the liver
normal range is 35-48 g/L
high levels
- indicates severity of liver disease
low levels = hypoalbuminaemia
- ascites due to oncotic pressure control
What is ascites? What is it caused by? How can it be treated?
ascites is condition where excessive free fluid is in the peritoneal cavity (space around the gut)
causes
- decreased colloidal plasma pressure due to decreased albumin synthesis by the liver
- sodium and water retention (RAAS)
- portal hypertension (can lead to oesophageal varices formation)
treatment
- low salt diet (40 mmol/day) and fluid restriction
- monitor weight
- bed rest
- spironolactone and/or furosemide
- severe ascites may require drainage
What does low albumin levels with no other LFT abnormalities suggest?
patients are likely to have a non-hepatic cause of low albumin
- malnourishment
- sepsis
- inflammation
What is prothrombin time? What is it used indicate?
looks at the time taken for blood to clot
- prothrombin is a coagulation factor (factor II)
it is an indicator of hepatic synthetic function
- does not become abnormal until 80% of liver synthetic capacity is lost
an elevated PT can result from a vitamin K deficiency
