Liver Function Tests Flashcards
What enzymes are tested for in a liver function test?
(ALT/AST) - serum transaminases
(ALP) - Alkaline Phosphatase
(GGT) - gamma glutamyl transpeptidase
What are the substances which are indications of the intrinsic synthetic function?
albumin
prothrombin time/INR
bilirubin
What are transamines?
Hepatic enzymes that are usually intracellular, but are released from hepatocytes in context of hepatocellular injury.
What reaction do transamonases catalyse?
y-amino group transfer e.g. aspartate or alanine to ketoglutarate
Give an example of an ALT and it’s properties
alanineamino transferase
- more sensitive than AST
- predominantly cytosol-located
- found mainly in the liver
- half life 47hrs
Give an example of an AST and its properties
aspartate aminotransferase
- in cytosol and mitochondria
- found in Liver, Heart, Pancreas, Skeletal muscle, Brain, Lungs, RBCs, WBCs
- Half Life Circa 17hrs
What can be learned from aminotransferase levels?
- deranged in most aetiologies
- increase in hepatocellular pathologies
- sometimes levels effect level of damage
- obstructive jaundice usually less than 500U/L
What are alkaline phosphatases?
Enzymes that catalyzes the hydrolyses of a number of organic phosphate esters.
Half-life about 1 week; therefore often lag to rise and slow precipitation in resolution of pathology.
What is the indication of biliary cholestasis (decrease in bile flow due to obstruction or decreased secretion)?
High ALP
high alkaline phophatase
Where does alkaline phosphatase ALP originate from?
epithelial cells of the biliary tree ducts bone placenta intestine kidney
What is gamma glutamyl transpeptidase?
Enzyme involved in gluthionine metabolism, transfer of amino acids across cellular membranes and leukotriene metabolism
Why are GGTs useful when compared to ALPs?
they help determine whether the elevated ALPs are due to bone or liver damage
Where do GGTs originate?
liver kidneys bile duct pancreas gallbladder spleen heart brain seminal vesicle Not bone.
What is GGT used as a marker for?
liver or cholestatic disease
What can induce GGT elevation?
drugs particularly anticonvulsants and TCAs and Paracetamol. Diabetes mellitus pancreatic disease COPD renal disease alcohol consumption
What is the normal process for bilirubin?
Predominantly a breakdown product of Heme
Transported to liver bound to albumin
Uptake into the hepatocytes
Undergoes conjugation
Excreted via urine/faeces (Urobilinogen/Stercobilinogen)
What are 2 forms that bilirubin can be found in in blood tests?
conjugated and unconjugated
What clotting factors is the liver responsible for the synthesis of?
Factors 1,2,5,7,9,12,13
1 (fibrinogen) and 2 (prothrombin)
What does the PT measure?
conversion time from prothrombin to thrombin
What is elevated PT an indication of?
reduced synthetic functionality can also be a result of Drugs (inc Warfarin) Bile malabsorption causing relative Vit K deficiency Consumptive coagulopathies Congenital coagulopathy
What is one of the most important aspects of LFT history takings?
what has changed since the difference in measures - any and all medications
What LFT indicates hepatocellular injury?
ALT/AST> ALP
raised bilirubin
What LFT indicates cholestasis?
ALP>ALT/AST
raised bilirubin
What LFT indicates Prolonged Jaundice/Vit K, Malabsorption
& Hepatocellular Dysfunction?
Increased PT/INR
What is the problem with the albumin test?
It is a difficult measure of liver function when used in isolation
What is the normal AST:ALT ratio?
- 8, >2 suggests alcohol
- can give a picture of the hepatocellular picture
What diseases can cause a strange AST:ALT ratio so need to be ruled out?
Coeliac Disease Muscle disorders (Myositis, Rhabdomyolysis) Creatine Kinase (CK) Adrenal Insufficiency Anorexia Nervosa Thyroid Disorders
What causes an increase in unconjugated bilirubin?
Increased bilirubin production
Impaired hepatic bilirubin uptake
Impaired bilirubin conjugation
What can cause increased bilirubin production?
Extra/intravascular haemolysis
Extravasation of blood into tissues
What can cause impaired hepatic bilirubin uptake?
Heart Failure
Portosystemic Shunts
Drugs; Rifampicin, Probenecid
What can cause impaired bilirubin conjugation?
Gilbert’s/CN Type II
Hyperthyroidism
Advanced Liver Disease
What can cause an increase in conjugated bilirubin?
Extrahepatic Cholestasis (Biliary Obstruction)
Intrahepatic Cholestasis
Drugs
What drugs can cause an increase in conjugated bilirubin?
Alkylated Steroids
Chlorpromazine, herbs, Rifampicin
What can cause Extrahepatic Cholestasis (Biliary Obstruction)?
Cholelithiasis Primary Sclerosisng Cholangitis Cholangiocarcinoma Head of Pancreatic Tumour Acute/Chronic Pancreatitis
What can cause Intrahepatic Cholestasis?
Sepsis/Hypoperfusion states Cirrhosis Infiltrative Diseases TPN Acute Hepatitis
