A Liver Function Test (LFT) is actually a group of blood tests that give insight into how well your liver is functioning. A liver function test can detect a range of substances in the blood including different proteins and enzymes that are produced by liver cells or released when these cells become damaged. It can be ordered if liver disease has been diagnosed or is suspected or to further investigate symptoms such as jaundice, dark urine, fatigue or lethargy, nausea, loss of appetite or abdominal pain.
LFTs encompass tests that are specific to a protein or enzyme, and when these multiple tests are ordered together, their results may help piece together a puzzle to provide insight as to what may be going on with your liver health.
What is being tested?
A Liver Function Test (LFT) can detect a range of substances in the blood including different proteins (such as albumin and total protein) and enzymes (such as ALT, AST, ALP and GGT) that are produced by liver cells or released when these cells become damaged. Some common enzymes and proteins the tests look for include:
- Alanine aminotransferase (ALT): measures levels of the ALT enzyme which metabolises protein and is found mainly in the liver. ALT is typically found at a low level and high levels may be an early indication of liver disease.
- Aspartate transaminase (AST): an enzyme relates to the function of bile ducts but is found in many other areas of the body.
- Alkaline phosphate (ALP): ALP is an enzyme that can be found in the liver, bones, bile ducts, heart and other muscles. It is often ordered in conjunction with other LFTs.
- Albumin and total protein: Albumin is an essential protein synthesised by the liver, where the level of albumin in your bloodstream indicates how well the liver is functioning. Total protein tests measure both albumin and all other proteins in the blood including antibodies that make up part of the body’s immune system.
- Total bilirubin: Bilirubin is a yellow pigment that can be found in the blood that is formed as a waste product of spent red blood cells. It passes through the liver before being removed from the body.
- Gamma-glutamyl transferase (GGT): GGT is an enzyme that is found in the liver.
- Lactate dehydrogenase (LHD): LHD is an enzyme found in the liver.
How do I know what test I need, or which disease I should be screened for?
Your healthcare professional will be able to best determine which tests to order based on your symptoms and history. If you have been potentially exposed to a hepatitis virus, for instance, they may look at your ALT levels and may also require further tests that look for hepatitis antigens or antibodies. Further, LFTs may be ordered if you have added risk factors for liver dysfunction such as heavy consumption of alcohol, a family history of liver disease or the consumption of drugs that can damage the liver.
Symptoms that can also warrant LFTs include weakness, fatigue, nausea, vomiting, abdominal swelling or pain, jaundice, itching, loss of appetite and dark urine or light-coloured stools.
Diseases or conditions that could be indicated by LFTs include;
Hepatitis A, B and C
High levels of ALT can indicate liver disease and very high ALT levels may be due to an acute hepatitis infection.
Alcohol use disorder
The GGT enzyme can leak into the blood when the liver is damaged. Although high GGT levels are not limited to alcohol related liver disease, GGT levels are widely used as an indicator of heavy alcohol consumption.
Alongside a standard LFT, to investigate potential liver cancer a test may be ordered to detect the levels of alpha-fetoprotein (AFP) in the blood. Higher levels of AFP are seen in pregnancy but AFP is also a tumour marker for liver cancer.
An increase in the levels of ALT and AST seen in an LFT may be associated with type 2 diabetes.
Why do I need a liver function test?
Your healthcare professional may order an LFT if you are an at-risk individual for liver disease or damage, or if you are experiencing symptoms that may indicate liver disease such as jaundice, dark urine, pale stools, tiredness or weakness, loss of appetite, nausea and vomiting, abdominal pain or swelling or itching.
Preparing for the test
For the majority of pathology tests, no specific preparation is needed. If you are having a test you have not had before, check with your doctor or whoever ordered the test whether you need to fast, or if there are any foods you should avoid before the test. You should also let your doctor know any medications or supplements you are taking as this could affect the test results.
Do I need to fast before a liver function test?
Liver function tests do not usually require fasting, but for any pathology test it is best to discuss preparation with your health professional before the test.
What happens during the test?
In your local GP clinic or health service, most pathology samples will be taken by a trained pathology collector, also called a phlebotomist, or sometimes by a nurse. A blood test usually involves taking a sample from a vein in your arm.
The results of LFTs may help piece together a puzzle to provide insight on what may be going on with your liver health. If your LFT was ordered due to symptoms, then normal LFT results will help your doctor rule out liver problems and look for other causes. The meaning of abnormal LFT results will depend on a number of factors including your symptoms, individual circumstances and medical history. Your health professional will explain the results to you. They may request further pathology tests or refer you for other investigations such as diagnostic imaging or a specialist appointment.
All pathology test results are interpreted by a pathologist who provides a report to the General Practitioner, specialist doctor or other medical personnel who ordered the tests. The healthcare professional will use the pathology report and consideration of the clinical context to decide on the next steps for their patient. Test results, treatment and medical questions should always be discussed with your treating health professional.