Liver function tests (LFT) – in-depth information

Also called LTFs or hepatic function panel

Having a test can be worrying but knowing what to expect and being prepared can help. Here are the answers to some common questions people ask about liver function tests.

On this page, you can find the following information:

What is a liver function test (LFT)?

Liver function tests (LFTs) are a group of tests performed on a single blood sample to find out how well your liver is working. The test measures the levels of a number of proteins and enzymes that are either produced by liver cells or released into the blood when liver cells are damaged. The liver is a large organ in the upper right of the abdomen that is necessary for many different functions. For example, it processes drugs and alcohol, filters toxic chemicals, stores vitamins and minerals, and makes bile, proteins and enzymes.

Liver function tests measures the levels of different enzymes and proteins excreted by your liver, such as:

  • alanine aminotransferase (ALT) – an enzyme in your liver
  • alkaline phosphatase (ALP) – an enzyme in your liver
  • aspartate aminotransferase (AST) – an enzyme in your liver
  • gamma-glutamyl transferase (GGT) – an enzyme in your liver
  • bilirubin – a breakdown product of red blood cells that is excreted by your liver 
  • albumin – the main type of protein that your liver makes
  • total protein – the total amount of different proteins in your body.

(Lab Tests Online, Australia, 2018)

Why would I need a liver function test?

A liver function test is not done routinely but is requested in certain situations, to establish the presence of damage or inflammation in the liver. Your doctor may ask for this test to be done to:

  • screen for potential liver problems such as fatty liver and viral hepatitis
  • help in the diagnosis of other conditions, eg, gallstones
  • monitor the ongoing development and severity of liver disease and to determine how well a treatment is working
  • monitor side effects if you are taking prescription or non-prescription medicines that can affect liver functioning.

Your doctor might order LFTs if you have:

  • jaundice or dark urine or light-coloured bowel motion (poo)
  • weakness or tiredness
  • loss of appetite
  • nausea and vomiting
  • abdominal pain or swelling
  • itching.

How do I prepare for a liver function test?

Generally, you won't need to do anything before having this test. It can be done at any time of the day. Some medicines may affect the test so tell your doctor about all prescription and non-prescription medicines (such as herbal products, supplements and rongoā Māori) you take.

What does the test involve?

An LFT is a blood test which means a small amount of blood is taken by placing needle placed in a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight for a few seconds. You may feel nothing at all from the needle, or you may feel a small brief sting or pinch. The blood sample is collected in a tube, which is sent to the laboratory for analysis. Read more about blood tests.

What do my results mean?

Interpreting liver function test results is complicated and is best done in consultation with your healthcare team. Your healthcare provider will look at the pattern of abnormalities and combine that with your signs and symptoms to make a diagnosis. Often the test will need to be repeated to see if there is a pattern over time.  

The enzymes and proteins are divided into different categories which are used to help find the cause of any abnormal results.

Liver enzymes and proteins 
Aminotransferases
  • These are alanine aminotransferase (ALT) and aspartate aminotransferase (AST).
  • Some labs don’t measure AST routinely because ALT is more specific to the liver.
  • These enzymes are usually stored inside liver cells. However when liver cells are damaged they are released into the blood stream resulting in increased levels.
  • Common causes of raised levels are fatty liver due to obesity, alcohol, viral hepatitis and medications.
  • Rarer causes are the genetic condition haemochromatosis and certain autoimmune diseases.
Gamma-glutamyl transferase (GGT) and Alkaline phosphatase (ALP)
  • These are more specific to cholestasis. Cholestasis refers to the reduction of the flow of bile through the liver.
  • This can be due to alcohol (usually just GGT elevated), gallstones and medications.
  • Rarer causes are cancer and certain autoimmune conditions
Bilirubin
  • Bilirubin is produced during the normal breakdown of red blood cells.
  • Raised levels can lead to jaundice (yellow skin).
  • There are a large number of causes of raised levels.
  • If the other tests are normal and bilirubin is only mildly elevated the most common cause is a harmless condition called Gilbert syndrome.
Albumin 
  • Albumin is the most common protein in the bloodstream and it is produced by the liver.
  • One cause of low albumin is when the liver isn’t able to keep up with production.
  • This can mean severe liver disease, but poor nutritional intake, or severe illness are other common causes.
  • Your healthcare provider may also do a coagulation test called an INR because the liver also produces clotting factors (to make blood clots).

Liver function tests have some limitations. Abnormal values can be due to conditions not related to the liver. For example ALP is also found in bone, and may be raised in bone-related problems. Also in people with very severe liver disease the levels may be normal.

What should I do if the test is only mildly abnormal?

You should speak to your healthcare provider. If you otherwise feel generally well, the most common causes for elevated liver function tests are alcohol consumption and fatty liver due to obesity. Your healthcare provider may recommend you reduce the amount of alcohol you drink, maintain a healthy weight, stop smoking, exercise regularly and eat a healthy balanced diet. The test can be repeated in a few months to monitor your progress.

Learn more

The following is further reading that gives you more information on having a blood test and the liver function tests. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

Blood test safety information Labtests, NZ
Liver function tests Patient Info, UK
Liver function tests  Australasian Association of Clinical Biochemists

Credits: Health Navigator Editorial Team. Reviewed By: Dr Jeremy Steinberg, FRNZCGP Last reviewed: 06 Dec 2021