Liver Function Tests (LFTs) are a group of blood tests that can help show how well your liver is working. They measure several substances made by the liver including enzymes and proteins. Each substance gives different information. Looked at together, along with your symptoms and medical history, they help build a picture of your liver’s health. Either higher or lower than normal levels of these substances can indicate a problem with your liver.
Your doctor may order LFTs:
When performed together, these tests give a snapshot of the health of your liver, an indication of the potential severity of any liver injury, change in liver status over time, and a starting place for further diagnostic testing.
Usually, no one single set of liver tests is used to make a diagnosis. Often, several LFTs will be ordered over a few days or weeks to determine if a pattern is present and to help determine the cause of the liver disorder.
When liver disease is detected, it is often monitored on a regular basis with all LFTs or one or more of its components. LFTs can also be ordered regularly to monitor the effectiveness of treatment.
The liver – what it does
The liver is essential for digesting food and removing harmful substances from the blood. It changes the nutrients and chemicals in the blood into forms that are easier for your body to use. It metabolises and detoxifies drugs and substances that could be harmful. It also produces bile, which is a fluid that helps break down proteins, carbohydrates and fats so your body can use them. Bile is stored and concentrated in the gallbladder for later use. The liver also produces blood clotting factors, it controls the amount of blood in your body and stores glycogen for energy and vitamins. Importantly, the liver is a key component of the immune system removing potentially harmful bacteria and viruses from the body.
What causes liver damage?
The liver can be damaged by many things including viral infections or lifestyle behaviour such as alcohol and certain drugs.
Early liver disease often shows no symptoms or mild nonspecific symptoms, such as fatigue and nausea. But liver disease can cause inflammation, bile duct obstructions and clotting abnormalities. Over time, conditions that damage the liver can lead to scarring, known as cirrhosis, which increases the chance of liver failure, a life-threatening condition. Early treatment can give the liver the time it needs to heal.
Hepatitis is a term used for inflammation of the liver. It can be either acute or chronic:
Acute hepatitis is a fast developing disease and typically makes someone feel sick, as if they have the flu, often with loss of appetite and sometimes diarrhoea and vomiting. In many cases, acute hepatitis turns urine brown, and colours the skin and eyes yellow. Most people who are affected eventually recover completely in less than six months. Hepatitis A virus is the most common cause of acute hepatitis. Acute hepatitis is caused by certain drugs, alcohol, some immunological conditions or any condition that blocks the release of bile from the liver and impaired liver function during pregnancy.
Chronic hepatitis is classified as liver inflammation that lasts longer than six months. It usually causes no symptoms or only a loss of energy and tiredness. Most people don’t know that they have it. Chronic hepatitis can gradually damage the liver and, after many years, cause it to fail. It is usually caused by infection by hepatitis B or C virus, alcoholic liver disease and/or fatty liver.
Inherited conditions such as haemochromatosis and Wilson's disease can cause severe liver disease so it is important to tell your doctor of any family history of liver problems . Early detection of these conditions allows them to be treated and managed appropriately.
Tests used to assess your liver
If your doctor suspects liver disease, they will order a range of blood tests and scans to see if there is liver disease, determine the cause and the best form of treatment.
LFTs or one or more of the component tests of LFTs will be important to your diagnosis.
Abnormal LFT results may prompt repeat testing over a period of time. LFTs may also be ordered to monitor the effectiveness of any treatment you need to have, or lifestyle changes you make.
In order to diagnose a liver disease, your doctor will evaluate the LFTs results, order follow-up blood tests for specific liver diseases such as hepatitis or testing for certain genetic conditions. Imaging tests that can show liver damage include ultrasound, CT (computerized tomography) and MRI (Magnetic resonance imaging) scans. A liver biopsy maybe done to help confirm a diagnosis and assess the extent of liver damage.
Reading your test report
Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.
Results of LFTs are usually assessed together. Several sets of results from tests performed over a few days or weeks are often assessed together to see if there is a pattern. Your test results will typically change over time. Your doctor evaluates the combination of liver test results to gain clues about the underlying condition.
|Individual test components in a Liver Function Test panel|
|Alanine aminotransferase (ALT)||A very high level of ALT is often seen with acute hepatitis. Moderate increases may be seen with chronic hepatitis. People with blocked bile ducts, cirrhosis, and liver cancer may have ALT levels that are only moderately raised or close to normal.|
|Alkaline phosphatase (ALP)||ALP may be significantly increased with obstructed bile ducts, liver cancer, and with bone disease. Raised levels of both ALP and GGT indicates that liver disease is present rather than bone disease.|
|Aspartate aminotransferase (AST)||A very high level of AST is often seen with acute hepatitis. AST may be normal to moderately increased with chronic hepatitis. In people with blocked bile ducts, cirrhosis, and liver cancer, AST concentrations may be moderately increased or close to normal. When liver damage is due to alcohol, AST often increases much more than ALT (this is a pattern seen with few other liver diseases). AST is also increased after heart attacks and with muscle injury.|
|Bilirubin||Bilirubin is a yellow-coloured compound that is increased in the blood when too much is being produced or less is being removed, due to bile duct obstructions, or to problems with bilirubin processing. It is not uncommon to see high bilirubin levels in newborns, typically under three days old.|
|Albumin||Albumin is the main protein made by the liver and is often normal in liver disease but may sometimes be low due to decreased production or if it is lost through damaged kidneys|
|Total Protein||The total protein test measures albumin and all other proteins in blood, including antibodies. Total protein levels are typically normal with liver disease.|
|Gamma- glutamyl transferase (GGT)||A GGT test may be used to help decide the cause of an raised ALP. Both ALP and GGT are raised in bile duct and liver disease, but only ALP will be raised in bone disease. Increased GGT levels are also seen with alcohol consumption and often in people taking drugs that are metabolized in the liver such as carbamazepine and phenobarbitone.|
|Prothrombin Time (PT)||Prothrombin is a protein made by the liver. A prothrombin time (PT) test measures how long it takes for a blood to clot. A prolonged or increased PT can be seen with liver disease, vitamin K deficiency, and with coagulation factor deficiencies.|
Your LFT results cannot diagnose a specific disorder. They can only show that your liver may not be working as it should be.
If you do not have symptoms or identifiable risk factors, abnormal liver test results could mean there is:
Your results will be compared to reference intervals (sometimes called a normal range).
If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.
The reference intervals for all LFT's except GGT have common reference intervals which means that all laboratories in Australia should be using the same ranges for these tests.
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask: