Practical 6: Investigation of Liver dysfunction
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Why are certain markers seen in peripheral blood if a patient has liver damage?
These markers leak out of hepatocytes which have become damaged
What type of substances are measured in a liver function test? (4)
Those that are normally produced by the hepatocyte Those that are known to change when hepatocytes are damaged Those released from hepatocytes when they are damaged Those that assess the ability of the liver to perform tasks such as conjugation or detoxification
What are the two types of tests that make up a LFT?
Tests of function Test of hepatocellular damage
What are the tests of liver function (3)
Albumin, bile acids (synthesis) Total or conjugated bilirubin (excretion) Ammonia (detoxification)
What are the tests of hepatocellular damage? (4)
Alanine aminotransferase (ALT) Aspartate aminotransferase (AST) Alkaline phosphatase (ALP) y-Glutamyl transferase (GGT)
What are considered the two billary tree enzymes
Alkaline phosphatase (ALP) y-Glutamyl transferase (GGT)
What exactly is bilirubin
A hydrophobic breakdown product of haem
What is bilirubin conjugation?
The conversion of bilirubin into mono and diglucuronides by the liver
What is the function of bilirubin conjugation?
To increase the solubility of the bilirubin molecule
What happens to bilirubin once it has been conjugated? (2)
The majority is secreted into bile Some leaks out into the plasma
How can we determine the type of disease depending on the ratio of conjugated and free bilirubin in circulation?
If bilirubin can be conjugated but not secreted then the levels of conjugated bilirubin will increase in the circulation and the total bilirubin will also be increased
What is the principle behind the Bilirubin assay
Bilirubin reacts with diazotised sulphalinic acid to produce azobilirubin which is a reddish-purple colour
What does ALT stand for?
Alanine aminotransferase
What is ALT
An enzyme involved in amino acid metabolism which is found in the hepatocytes
When might ALT be seen in circulation
When there is an injury to the cells which disrupts hepatocyte integrity
What is the principle behind the ALT assay (3)
Based on the ability of ALT to break down alanine to form pyruvate LDH then converts pyruvate to lactate but with the conversion of NADH to NAD+ This fall in NADH is measured spectrophotometrically