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:
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.
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.
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Liver Blood Tests FAQs
The first thing to do is discuss with your GP why you have concerns – are you worried about past or present lifestyle risk factors, such as drinking too much alcohol, being overweight or a risk of viral hepatitis? Do you have a familyhistory of liver disease or symptoms you’re worried about? If your GP thinks it’s appropriate, they will perform a panel of routine liver blood tests and relevant care or treatment can be discussed from there. If there is an additional family history for a condition such as haemochromatosis, in which the body stores too much iron, your doctor will organise additional specialist tests.
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.
Abnormal liver blood test results are relatively common and most people with these results have normal liver function. An infection or a reaction to medication might affect your blood test results and sometimes a repeat liver blood test is all that’s needed. However, any abnormality does need to be investigated to find out what the cause is.
Scans may be performed to help understand the cause of the abnormality and also to assess how significant any damage is.
These may include imaging scans such as ultrasound, elastography scans such as FibroScan, CT or MRI scans , which help doctors get a better picture of the extent of any damage to the liver. In certain cases a liver biopsy (where a tiny piece of tissue is taken from the liver for examination) may be considered to specifically diagnose a condition or provide information on the extent of scarring inside the liver.
If you are very unwell, you may be referred or admitted to hospital, although this is unusual – only a very small number of people with abnormal liver blood tests require admission.
Your doctor will explain your test results to you. If they are abnormal, your doctor will also explain the most likely cause, and how severely affected your liver may be.
When a patient has been found to have an abnormal liver blood test, the next step is to establish the cause. This requires a second panel (set) of blood tests that look for potential causes such as viruses, problems with the immune system and rarer inherited conditions.
If I am found to have non-alcohol related fatty liver disease (NAFLD), what tests should I have next?
NAFLD is very common and 30-40% of the population have it. If you have NAFLD, the next step is to investigate the extent of the condition and if the liver is scarred or damaged. The level of scarring can be assessed using specialist scans or blood tests and your doctor can explain these to you.
If these tests are not able to assess any damage accurately, a liver biopsy may be considered to provide more detailed information.
Because NAFLD is commonly associated with being overweight, there is evidence to suggest that losing weight through diet and exercise helps reduce the amount of fat in the liver and damage done to it.
The Government advises that both men and women should not regularly drink more than 14 units in a week. It is also important to have 2-3 consecutive days off drinking a week to allow your liver to recover.
However, the National Institute for Clinical Excellence (NICE) guidelines recommend
that if you drink alcohol in a harmful way, defined as more than 50 units of alcohol per week for men (around 15 pints of beer) and 35 units for women (about 3.5 bottles of wine), and have done so for several months, you should have a non-invasive test for cirrhosis.
Not necessarily. If your results are abnormal your GP can advise you on the next steps to determine the cause and assess how serious the problem and any associated damage is.
You need to see specialists at this point, which your doctor will arrange. A specialist team will then do more tests to get a better idea of what’s wrong with your liver, and how best to treat it.
Please download the Liver Disease Tests Explained publication for further information.
Liver disease tests explainedDownload