Liver Function Tests Flashcards
Describe the blood supply of the liver
- Has a “double” blood supply o Hepatic artery – oxygenated blood o Portal vein – nutrient rich blood
What is the functional unit of the liver
- Functional unit = liver lobule
Describe a liver lobule
- Each lobule is hexagonal in shape and composed of: hepatocyte (parenchymal cells) arranged in plates, in contact with bloodstream on side and bile canaliculi (“little canals”) on the other
What is between plates within the liver?
- Between the plates are vascular spaces (sinusoids) containing Kupffer cells (phagocytic macrophages)
What are the main functions of the liver?
- Metabolic Functions – carbohydrates, hormones, lipids, drugs and proteins - Storage – glycogen, vitamins, iron - Protective – detoxification and elimination of toxic compounds, Kupffer cells ingest bacteria and other foreign material from blood - Bile production and excretion – formed in biliary canaliculi, emulsifies fats and provides route for waste removal
What is the main types of disease of the liver?
- Infection – viral (hepatitis A-E, CMV), bacterial, parasitic - Toxic/Drug induced - Autoimmune - Biliary tract obstruction – tumours, gallstones - Vascular - Metabolic – hemochromatosis, Wilson’s, hereditary hyperbilirubinemias
What are the main causes of acute hepatitis?
o Poisoning (paracetamol) o Infection (hepatitis A-C) o Inadequate perfusion
What are the main outcomes of acute hepatitis ?
o Resolution – majority of cases o Progression to acute hepatic failure o Progression to chronic hepatic damage
What are the common causes of chronic liver disease?
o Alcoholic fatty liver o Chronic active hepatitis o Primary biliary cirrhosis
What are the unusual causes of chronic liver disease?
o -1 AT deficiency o Haemochromatosis o Wilson’s disease
Cholestasis =
failure to produce or excrete bile
What is the result of cholestasis?
- Result is accumulation of (conjugated) bilirubin in the blood leading to jaundice
Give another cause of jaundice except cholestasis
excessive haemolysis – bilirubin is unconjugated and does not appear in the urine
What are the main classifications for liver failure?
- Inadequate synthesis of albumin leading to oedema and ascites
- Inadequate synthesis of clotting factors resulting in bruising - Inability to eliminate bilirubin causing jaundice
- Inability to eliminate nitrogenous waste e.g. ammonia, giving rise to hepatic encephalopathy, a poorly defined neuro-psychiatric disorder
What are the 4 main current liver functions tests
Albumin - For synthetic function ALT (& AST) - Aminotransferases for hepatocellular damage ALP (& -GT) - for biliary epithelial damage & obstruction Bilirubin - For cholestasis (bile flow blockage)
What are the advantages of LFTs?
o Cheap, widely available, interpretable o Direct subsequent investigation (e.g. imaging)
What are the disadvantages of liver function tests?
o Do not assess liver “function” o Lack of complete organ specificity o May be “over-sensitive” o >40 years old, many newly discovered diseases for which they have no diagnostic value
What is albumin?
main plasma protein
When can low albumin be found?
o Post-surgical/ITU patients’ due redistribution o Significant malnutrition o Nephrotic syndrome
What do ALT and AST indicate?
non-specific markers of acute damage to hepatocytes
Where are ALT and AST found outside the liver?
Cytoplasmic enzymes also found in cardiac muscle & erythrocytes
When is ALP increased in liver disease?
increased in liver disease due to increased synthesis in response to cholestasis
Where is ALP also present?
Also present in bone, gut and placenta
When is -GT raised?
raised in cholestasis, also affected by ingestion of alcohol and drugs such as phenytoin
