Week 5 Liver Tests KCP Flashcards
In a liver function test what is ALT / AST
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are enzymes found within liver cells at high concentrations.
Raised ALT / AST levels in the blood occur in pathologies that cause liver cell (hepatocyte) inflammation or damage. Therefore, raised ALT / AST levels are a marker of hepatocellular injury.
Hint: HIPatocytes are alternative and can’t be arst
In a liver function test what is ALP
Serum alkaline phosphatase (ALP) is derived from biliary epithelial cells (cells lining the biliary tract) and bones. Raised ALP levels can therefore be caused by cholestasis or bone disease.
Hint: The billirubin flow down from the Alps
What is Cholestasis
Blockage of bile flow, normally due to gallstones
In a liver function test what is GGT
Gamma-glutamyltransferase (GGT) is found in hepatocytes and also biliary epithelial cells.2 It is a non-specific but highly sensitive marker of liver damage and cholestasis.
Hint: It’s a sign of both types of damage - gg patient wp
In a liver function test what is Bilirubin?
Bilirubin is a waste product of haemoglobin breakdown. It is predominantly metabolised and excreted by the liver. Raised levels of bilirubin in the blood will lead to a yellowing of the skin, known as jaundice.
Raised levels of bilirubin in the blood can be caused by:
- Excess bilirubin production (pre-hepatic jaundice)
- A breakdown in bilirubin metabolism (hepatocellular jaundice)
- A blockage in the bile excretion pathway (cholestatic jaundice)
Describe the bilirubin metabolism pathway
- When red blood cells are broken down, unconjugated (insoluble) bilirubin is created as a waste product and binds to albumin in the bloodstream
- Hepatocytes take up unconjugated bilirubin and metabolise it to form conjugated (soluble) bilirubin
- Hepatocytes excrete conjugated bilirubin into the biliary tract, where it flows into the bowel lumen as bile
- Gut bacteria further metabolise bilirubin in bile to form urobilinogen, which is eventually excreted in the stools as stercobilinogen
- A small amount of urobilinogen is reabsorbed from the intestine into the portal venous system, and as urobilinogen is water-soluble, the kidney is able to excrete some of this into the urine.
In a liver function test what is Albumin a sign of?
Albumin is synthesised in the liver and helps to bind water, cations, fatty acids and bilirubin. It also plays a crucial role in maintaining the oncotic pressure of blood. Albumin is used as a non-specific marker of the synthetic function of the liver.
Albumin levels can fall due to:
Decreased albumin production: malnutrition, severe liver disease
Increased albumin loss: protein-losing enteropathies, nephrotic syndrome
What 6 things do we look out for in a liver function test?
ALT
AST
ALP
GGT
Bilirubin
Albumin
What does a rise in bilirubin only infer?
- Gilberts synd: Gilbert’s syndrome is a common, benign liver condition where the liver doesn’t process bilirubin as efficiently, leading to slightly elevated levels in the blood
- Elavated Haemolysis
What is more liver specific ALT or AST?
Alanine transaminase (ALT), more liver specific than aspartate transaminase (AST).
Would would AST>ALT tell you?
ALD (alcoholic liver disease) or advancing fibrosis
Do LFTs reflect damage or function?
They reflect damage not function despite the name
What specific conditions result in increase GGT?
- alcohol
- obesity
- phenytoin
- carbamazipine
- NAFLD cirrhosis
At what point might you start to see raised albumin?
Often normal in cirrhosis until liver failing
Not a good marker of acute liver failure
LFT Patterns:
- Bil only
- ALT mild
- ALT high
- GGTP only
- ALK Phos+GGTP
- 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
