Liver Function Tests Flashcards
why are LFTs checked?
investigate for liver disease
monitor current liver disease
monitor effects of hepatotoxic medication (methotrexate/DMARDs)
what LFTs test liver inflammation and damage?
ALT (alanine aminotransferase)
AST (apartate aminotransferase)
GGT (gamma glucuronic transferase)
Bilirubin
what LFTs test for impairment of liver synthesis?
albumin
glucose (lack of glucogenesis)
PT time/ratio
describe the enzymes ALT and AST as LFTs
raised during hepatocellular injury (hepatitis, cirrhosis, drug/toxin induced, malignancy)
AST:ALT ratio determines cause of hepatocellular injury (>2:1 suggestive of alcohol related)
describe ALP and GGT as LFTs
ALP = serum alkaline phosphatase, derived from biliary epithelial cells and bones
GGP = non-specific/highly sensetive cholestasis marker
ALP/GGT interpreted together
ALP increased, GGT normal = bone disease (pagets/vit D deficiency)
ALP and GGT increased = cholestasis
what is cholestasis?
interruption in bile flow from hepatocytes to SI
explain what bilirubin is
waste product of haemoglobin breakdown
metabolised/excreted by liver
conjugated in the biliary tract and enters SI lumen in bile
what are the causes of increased bilirubin?
excess bilirubin production (pre-hepatic jaundice)
reduction in bilirubin metabolism (hepatocellular/hepatic jaundice)
blockage in bile excretion pathway (cholestatic jaundice)
explain hepatocellular/hepatic jaundice
damaged hepatocytes, inability to metabolise unconjugated bilirubin (builds up in blood)
high ALT/AST levels marking hepatocyte damage
what are the causes of unconjugated hyperbilirubinaemia?
pre-hepatic jaunduce (haemolysis)
gilbert syndrome (genetic)
what are the causes of conjugated hyperbilirubinaemia?
cholestasis
hepatocellular jaundice
explain cholestatic jaundice
interruption in bile flow
conjugated bilirubin builds up in blood
ALP/GGT high (biliary system issue)
causes dark urine and pale stools
what are the 2 types of cholestasis?
intrahepatic (obstruction of hepatic bile canaliculi)
extrahepatic (obstruction of hepatic ducts/distal biliary tree)
what are the causes of intrahepatic cholestasis?
hepatitis (viral A-E/autoimmune)
cirrhosis
malignancy
drugs (antibiotics/steroids/anabolic steroids/contraception)
pregnancy
what are the causes of extrahepatic cholestasis?
gallstones
primary sclerosing cholangitis
intraluminal malignancy (cholangiocarcinoma)
extraluminal malignancy causing duct compression (pancreas head tumours)
