Liver blood tests look at how well the liver is functioning and can indicate whether there is any damage or inflammation inside the liver. Until recently, liver blood tests were referred to as liver function tests, or LFTs. However, as most patients with abnormal liver blood tests actually have normal function of the liver, this term was felt to be unhelpful and often led to unnecessary concern. Therefore the term liver function tests, or LFTs, has been replaced by liver blood tests. This is a very important change, and the medical profession is working hard to ensure the new term is widely accepted and used.
Calling these tests liver blood tests is a more accurate way of describing what the test actually does and uses less frightening language.
What happens when I have a liver blood test?
When you have a liver blood test, a syringe with a fine needle is used to remove a small amount of blood from a vein in your arm. The sample can be taken by your GP or a nurse at your local clinic, or by hospital staff (a person who is specially trained to take blood is called a phlebotomist). It will then be sent to a laboratory to be tested.
What is a liver blood test looking for?
A liver blood test looks at the chemicals (enzymes), proteins and other substances made by the liver to assess whether levels of any of these are abnormal. The main ones are:
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST)
ALT and AST are enzymes found in the liver cells (hepatocytes) which leak into the blood stream when the liver cells are damaged. They indicate the degree of inflammation present in the liver. Levels of ALT and AST are usually high in conditions such as hepatitis – possibly twenty to fifty times higher than normal. The ALT ‘value’, or level, is more specific to the liver than the AST value because the AST value may also be high if there is muscle damage elsewhere in the body. Monitoring levels of these enzymes can help doctors
assess how much liver scarring (fibrosis) there is in conditions such as non-alcohol related fatty liver disease (NAFLD) and alcohol-related liver disease.
Alkaline phosphatase (ALP) and y-Glutamyltransferase (GGT)
These are enzymes found mainly in the bile ducts of the liver. Increases in ALP and another liver enzyme called y-Glutamyltransferase (GGT) can indicate obstructive or cholestatic liver disease, where the flow of bile from the liver is blocked because of an obstruction of the bile duct. GGT levels are also a potential indicator of how much alcohol a patient drinks and can also be higher in those with non-alcohol related fatty liver disease (NAFLD).
Bilirubin is produced when red blood cells break down, and is the main pigment in bile (a yellow/green substance made by your liver that aids digestion). An increase of bilirubin causes jaundice, characterised by a yellowing of the eyes and skin in liver disease.
This is a protein made by the liver that makes up about 60 per cent of total protein in the blood, helping to maintain tissue growth and repair. It stops fluids from leaking out of blood vessels and carries nutrients and hormones around the body. Albumin levels may decrease if the liver is damaged.
The levels of each of these will be given in numbers and values. The laboratory where the blood is being tested provides a ‘normal value’ or ‘reference value’ against which your test results are measured. This is a broad range into which people without liver disease will fall. An abnormal liver blood test result is defined as being below or above the normal range.