Liver function tests are blood tests that measure substances that the liver produces. Doctors can use these results to evaluate the health of a person’s liver.
The liver serves several essential functions that support a person’s overall health and well-being. It removes toxins from the blood, metabolizes fats and proteins, and regulates blood clotting.
Viral infections, medications, genetic disorders, heavy alcohol consumption, and obesity can cause inflammation and damage in the liver. Continuous liver damage can lead to the formation of scar tissue, which can progress into a severe condition called cirrhosis.
Liver disease causes nearly 2 million deaths each year globally. However, early stage liver disease does not always cause symptoms.
This article explores liver function tests in more detail, including their uses and how to interpret the results.
Liver function tests, or liver panels, measure the levels of proteins, enzymes, and waste materials (bilirubin) in a person’s blood.
Doctors use these tests when they want to evaluate the health of a person’s liver or identify the cause of liver damage.
Liver function tests
- Alanine transaminase (ALT), which is an enzyme found in liver and kidney cells. ALT helps create energy for liver cells. Damaged liver cells release ALT into the bloodstream, which can elevate ALT levels in the blood.
- Aspartate transaminase (AST), which is an enzyme in the liver and muscles that helps metabolize amino acids. Similarly to ALT, elevated AST levels may be a sign of liver damage or liver disease.
- Alkaline phosphate (ALP), which is an enzyme present in the blood. ALP contributes to numerous vital bodily functions, such as supplying nutrients to the liver, promoting bone growth, and metabolizing fat in the intestines.
- Gamma-glutamyltransferase (GGT), which is an enzyme that occurs primarily in the liver, but it is also present in the kidneys, pancreas, gallbladder, and spleen. Higher than normal concentrations of GGT in the blood may indicate alcohol-related liver damage. Elevated GGT levels can also
increase the risk of developing cancer, particularly colorectal and liver cancers.
Liver function tests may also measure other compounds, such as:
- Bilirubin, which is a waste product that forms when the liver breaks down red blood cells. Bilirubin exits the body as bile in stool. High levels of bilirubin can cause jaundice — a condition in which the skin and whites of the eyes turn yellow — and may indicate liver damage.
- Albumin, which is a protein that the liver produces. The liver releases albumin into the bloodstream, where it helps fight infections and transport vitamins, hormones, and enzymes throughout the body. Liver damage can cause abnormally low albumin levels.
- Prothrombin time (PT) measures how long it takes for the blood to clot. A prolonged PT may be a sign of certain blood-clotting disorders related to liver damage.
Doctors use liver function tests to evaluate the health of a person’s liver. If a doctor suspects someone has liver disease or liver damage, they may perform one or more liver function tests to identify the underlying cause.
Symptoms of liver disease can include:
- nausea and vomiting
- loss of appetite
- unintentional weight loss
- pain in the upper right part of the abdomen
- swelling in the feet, ankles, or calves
- jaundice, or yellowing of the eyes and skin
- dark urine
Doctors may recommend one or more liver function tests for people who:
- have been exposed to or have a history of hepatitis A, B, or C infections
- are currently receiving treatment for liver disease
- currently take medications that affect the liver
- show signs of liver damage
- have alcohol use disorder
- have a family history of liver disease
- have a history of intravenous drug use
- have obesity
Healthcare professionals perform liver function tests on blood samples. A blood draw is a quick and straightforward procedure.
During a blood draw, a healthcare professional will disinfect the skin above a large vein in the arm. They may tie an elastic band, called a tourniquet, a few inches above the puncture site, which will increase the pressure inside the vein.
Once the healthcare professional can see the vein under the skin, they will insert a hollow needle at a
After collecting the blood sample, they will release the tourniquet, remove the needle, and press a cotton ball or gauze strip on the puncture site.
The healthcare professional will replace the cotton ball or gauze with a new one and apply an adhesive bandage over the puncture site. People can go home after having their blood drawn.
The blood sample will go to a laboratory for analysis. A doctor may discuss a person’s results over the phone or schedule a follow-up appointment.
Liver function tests reveal different information about the liver, depending on the specific substance a doctor is testing for.
The table below contains the
| Test | Typical levels | Atypical results |
|---|---|---|
| ALT | 4 to 36 international units per liter (IU/L) | Higher than usual results are a sign of:
|
| AST | 5 to 30 IU/L | Higher than usual results are a sign of:
|
| ALP | 30 to 120 IU/L | Higher than usual results are a sign of:
Lower than usual results are a sign of:
|
| GGT | 6 to 50 IU/L | Higher than usual results are a sign of:
|
| Bilirubin | 2 to 17 micromoles per liter (mcmol/L) | Higher than usual results are a sign of:
|
| Albumin | 35 to 50 grams per liter (g/L) | Higher than usual results are a sign of:
|
| PT | 10.9 to 12.5 seconds | Longer than usual results are a sign of:
|
Doctors use liver function tests to evaluate the health of a person’s liver. Atypical results
However, certain medications, lifestyle factors, and other underlying medical conditions can influence liver function test results.
Doctors may choose to investigate abnormal test results using:
- imaging tests, such as a CT scan or ultrasound
- a liver biopsy
- a blood count test
- tests for viral infections
- cholesterol and triglyceride testing
- genetic testing
- autoimmune tests
The exact type of treatment a person receives will vary depending on the underlying cause.
For example, a doctor may recommend that people who have liver damage due to alcohol use disorder need to stop consuming alcohol.
A doctor might recommend dietary and lifestyle changes to people who have nonalcoholic fatty liver disease.
Doctors can prescribe medications that treat viral hepatitis infections, autoimmune hepatitis, and conditions that damage the bile ducts.
Severe liver damage can cause complications, such as portal hypertension, that may require surgery or a liver transplant.
Many people do not realize they have liver disease until they have significant liver damage. As a result, doctors may order liver function tests as part of a regular health screening. These tests measure the levels of liver proteins, enzymes, and bilirubin in a person’s blood.
Atypical liver function test results may provide the first indications of liver disease. However, atypical results can also occur as a result of taking certain medications, viral illnesses, lifestyle factors, and other health conditions.
These tests do not often identify the underlying cause, but doctors can use them to plan their next steps.