The liver function test (LFT) is a blood test which measures the levels of several substances (enzymes and proteins) that are excreted by the liver. Levels that are higher or lower than normal can indicate liver problems.
- The liver function test (LFT) is also called a hepatic function panel (hepatic refers to the liver).
- The liver function test is done to establish the presence of damage or inflammation in the liver. It is not done routinely but is requested in certain situations, such as, to screen for any potential liver diseases if you have symptoms, to monitor for side effects if you are taking medicines that can affect your liver function or when you have liver disease, to monitor the progression and severity of the disease, and to determine how well a treatment is working.
- To perform a liver function test, a blood sample is drawn from a vein in the arm, and collected in a tube. This tube is sent to the laboratory for analysis.
What is a liver function test (LFT)?
The liver function test measures the levels of different substances (enzymes and proteins) that are excreted by the liver such as:
- alanine aminotransferase (ALT)
- alkaline phosphatase (ALP)
- aspartate aminotransferase (AST)
- gamma-glutamyl transferase (GGT)
- total protein.
When is a liver function test done?
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 such as:
- If you have symptoms, to screen for any potential liver problems or infections affecting the liver such as hepatitis A, hepatitis B and hepatitis C.
- To aid in the diagnosis of other conditions such as gallstones.
- When you have liver disease, to monitor the progression and severity of the disease, and to determine how well a treatment is working
- To monitor side effects, if you are taking prescription, or non-prescription medicines that can affect your liver function.
How to prepare for the test
For the most part, you do not need to do anything before having this test, and it can be done at any time of the day. Some medicines may affect the liver function test. Tell your doctor about all prescription and non-prescription medicines (such as herbal products) you take.
How is the sample collected for testing
A blood sample is taken by a needle placed in a vein in the 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.
Interpreting liver function test results is not always easy and is best done in consultation with your healthcare team. They will know what is normal for you and how these results relate with your clinical picture. Often, if there is a mild abnormality, all that may be needed is to repeat the test in a month or two's time as many changes can be temporary and return to normal.
On its own, a liver function test cannot usually provide a definitive diagnosis of a condition, but it can provide important "clues" about possible problems with your liver, such as:
- alanine aminotransferase (ALT) — when the liver is damaged, ALT is released into the bloodstream and levels increase.
- alkaline phosphatase (ALP) — higher than normal levels may indicate liver damage or disease, such as a blocked bile duct, or certain bone diseases.
- aspartate aminotransferase (AST) — an increase in AST levels may indicate liver damage or disease.
- bilirubin — bilirubin is produced during the normal breakdown of red blood cells. Elevated levels of bilirubin (jaundice) may indicate liver damage or disease.
- albumin and total protein — lower than normal levels of albumin and total protein may indicate liver damage or disease.
- gamma-glutamyl transferase (GGT) — higher than normal levels may indicate liver or bile duct damage.
The following is further reading that gives you more information on the full blood count test. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.