Liver function tests are tests of blood chemistry that can detect changes in the way the liver is making new substances and breaking down and/or excreting old ones. The tests can also show whether liver cells are healthy or damaged.
Bilirubin is the yellow breakdown product of red blood cells that is passed to the liver and excreted in bile. It is this substance that gives the yellow colour to the skin in jaundice. High blood bilirubin levels may indicate excessive breakdown of red blood cells, obstruction to bile flow, defective processing of bile by the liver, or Gilbert’s syndrome.
Albumin is one of the main proteins in blood. Made by the liver, one of its actions is to hold fluid inside the blood vessels. A low level is found in many chronic liver disorders and is often associated with ascites and ankle oedema (fluid collection in the abdomen and around the ankles).
Serum alkaline phosphatase
Alkaline phosphatase is an enzyme found in the cells that line the bile ducts and also in other tissues such as bone. The blood level of this enzyme rises when there is obstruction to the flow of bile (cholestasis).
An enzyme present in liver cells. When the flow of bile is obstructed, the blood level of this enzyme is raised, along with a raised level of alkaline phosphatase. A gamma-glutamyl transpeptidase level raised in isolation is related to alcohol intake. its measurement can also be used as a screening test for glutamyl transpeptidase deficiency.
Serum aminotransferases (transaminases)
The aminotransferases are enzymes released from liver cells into the blood when the liver cells are damaged. The levels will be raised in any condition that damages liver cells, including poisoning, and acute and chronic hepatitis.
A normal result in this test of blood clotting depends on the presence in the blood of a protein made by the liver from a fat-soluble vitamin, vitamin K. The test result can be abnormal in two types of disorder: when the protein is not made because of liver cell damage, and when there is a blockage to bile flow in the liver, causing a lack of bile in the intestines (which interferes with fat and vitamin K absorption).