Abnormal Liver Function Tests Flashcards
Describe the liver
-Approx 1.5 kg
-in ‘chest`
-2 blood supplies;
-art ^ press+low O2, PV low press,low O2
Overview of liver function tests
Not sensitive or specific
reflect damage rather than function
BUT clinically useful
AND patterns give clues
Describe bilirubin
-difficult to assay and non-specific
-haem–biliverdin–bilirubin——>
-mono then diglucuronide–bile–stool—->
-some reabsorbed as urobilinogen
-Isolated rise in Gilberts synd. Or haemolysis
Describe the pathway of bilirubin excretion
-Because of its poor solubility in physiologic
aqueous solution, unconjugated bilirubin circulates in the blood as a noncovalent complex with albumin.
-The pores in the hepatic sinusoids are
sufficiently large so that the bilirubin-albumin complex readily diffuses to the plasma membrane of the hepatocyte as blood flows through the liver.
-It is there unconjugated bilirubin dissociates from albumin and enters the cytosol. This dissociation occurs by facilitated transport.
-Within the hepatocyte cytosol, unconjugated bilirubin is bound to the protein ligandin (glutathione-S-transferase).
-The bilirubin molecule is subsequently conjugated with one or two molecules of glucuronic acid by the enzyme uridine diphosphate-glucuronyl
transferase, which is located in the interior of the endoplasmic reticulum
-Conjugated bilirubin is excreted across the canalicular membrane into bile.
-Conjugated bilirubin remains largely intact during passage through the biliary tract and the small intestine, but it is degraded by colonic bacteria to a series of tetrapyrroles that are collectively termed urobilinogen.
-These compounds partially account for the colour of stool. A portion of urobilinogen is absorbed and excreted in bile; less than 2% is excreted in urine under normal circumstances.
Describe ALT
-Alanine transaminase (ALT), more liver specific than aspartate transaminase (AST).
-half-life hours
-increased when hepatocytes die
-all dead=10,000, 10%=1000, 1%=100,
-0,5%=N (20 yrs min injury–> cirrhosis)
-AST>ALT in ALD or advancing fibrosis
Describe ALP
-Alkaline Phosphatase, liver only one of 4 isoenzymes (ie not specific)-check GGTP
-from biliary system-new enz production
-little reflects completeness of bile obstr
Describe GGT
-Gamma Glutamyltranferase, not just in liver ie not specific.
-Increases by induction not damage
-from liver and biliary system
-^ alcohol, obesity, phenytoin, carbamazipine, NAFLD cirrhosis
Describe Albumin
-Large amount in blood
-Important for osmotic effect, carries non-water soluble subst incl uncon bil
-High in dehydration
-Low due to dilution or reduced synth
-Often normal in cirrhosis until liver failing
Describe prothrombin time
-Good marker of synthetic function of the liver
-Very good in acute liver failure
-Rarely very abnormal in cirrhosis
What do patterns in liver function tests reflect?
-Bil only–Gilbert’s or haemolysis
-ALT mild–common eg NASH, hepC, ALD incl Alc Hep.
-ALT high– hepatitis incl drug damage
-GGTP only– induction eg drug, inactive cirrhosis
-ALK Phos+GGTP biliary dis eg stones, panc ca, PBC
What other tests are done in response to abnormal liver function tests?
-In practice triggers a ‘liver screen’ with
-Hepatitis viruses
-Autoantibodies ANA, AMA and AntiSMAb
-Ferritin
-Caeruloplasmin and Alpha-1-antitrypsin
-Immunoglobulins
-And an ultrasound scan and referral
Raised bilirubin
-Occurs earlier in natural history of biliary disease (PBC) than in disease of liver parenchyma (cirrhosis)
-Swelling of liver within capsule in inflammation can impair bile flow (disproportionate rise to degree of liver damage)
Low serum albumin
-Liver disease
-Change in the volume of distribution of albumin, and reduced synthesis
-Can be normal in acute liver failure (plasma half-life 2 weeks)
-Reduced in chronic liver failure
ALT and AST
-Located in cytoplasm of hepatocyte (AST also in hepatocyte mitochondria)
-Expression of ALT outside the liver is relatively low= more specific for hepatocellular damage
-Hepatic LTFT pattern
ALP
-Alkaline phosphatase= enzymes that hydrolyse phosphate esters at alkaline pH
-Main sites of production are in liver, GI tract, bone , placenta and kidney
-Cell membranes of hepatic sinusoids and biliary canaliculi
-Levels rise with intrahepatic and extrahepatic biliary obstruction, sinusoidal obstruction (infiltrative liver disease)
GGT
-Gamma-glutamyl transferase= microsomal enzyme
-Highest concentrations located in liver, produced by hepatocytes and epithelium lining small bile ducts
-Cholestatic/ obstructive pattern with ALP
-Isolated= alcohol/ NAFLD
