Liver Function Tests

What are liver function tests?

Liver function tests are blood tests that measure different substances produced by your liver. These measurements give your healthcare provider important information about the overall health of your liver and how well it’s working. A liver panel will often measure several substances in one blood sample. It may include various enzymes, proteins and byproducts.

What are the five primary liver function tests?

The most common liver tests include:

• Liver enzymes test. Your liver enzymes include alkaline phosphatase (ALP), alanine transaminase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transferase (GGT). These are elevated when there’s liver injury.
• Total protein test.A total protein test measures levels of protein in your blood. Your liver makes protein, and low protein levels may indicate that your liver isn’t functioning optimally.
• Bilirubin test. Bilirubin is a waste product that your liver deposits in bile.
• LDH test. Lactate dehydrogenase (LDH) is an enzyme found in many of your body’s tissues, including your liver.
• Prothrombin Time (PT) test. This test measures how long it takes for a sample of your blood to clot, a process that involves proteins that your liver produces.

These tests are all part of a routine blood panel called a comprehensive metabolic panel.

When are tests done to check liver function?

Your healthcare provider might want to check these values to screen you for possible hepatitis or other liver diseases. If they already know that you have liver disease, they might want to check how it’s progressing or whether a treatment is working. You may also have a liver test to monitor the side effects of certain medications that are known to affect your liver.

What kinds of things can a liver panel tell you?

Different values and ratios of different substances may tell your healthcare provider:

• If you have liver inflammation (hepatitis).
• Whether the inflammation is alcohol-related or nonalcoholic (metabolic).
• Whether you have a problem in your liver itself or in your bile ducts.
• If your liver function is impaired, and if so, how much.
• If your bile flow is impaired, and if so, how much.
• Whether your medications are affecting your liver, and if so, how much.

How do liver function tests work?

A healthcare provider draws a small amount of blood from a vein in your arm to test in the lab. They’ll look for abnormally high or low levels of different substances. Often, they’ll want to compare levels of different enzymes or proteins to each other. If the balance is off, that can help them understand better what may be going on in your liver.

What happens during the test?

You may have the test at a hospital or a specialized testing facility. Your healthcare technician will locate the vein in your arm that they’ll use to draw blood from and then clean the site. They may wrap your arm with a compression band to make your veins stick out. They’ll insert a small needle into your vein and draw blood into a vial. It only takes a few minutes.

What happens after?

Your technician will send your blood sample to a lab for analysis. The lab may be in the same facility or a different one. This may determine how fast your results come back. It may be a few hours or a few days. As long as you aren’t feeling lightheaded from the blood draw, you can go home now, resume your medications and have something to eat and drink.

How do I interpret the results of my liver function test?

When you get your test results back, you’ll see different values listed for different substances that were measured. You’ll be able to compare low or elevated levels against normal values. But what do these numbers mean? Interpretation of your liver function test takes some skill. Your healthcare provider will walk you through your results and how to read them.

What is the normal range for liver function tests?

Normal ranges vary between different sexes and body sizes, as well as between different laboratories. On average, normal ranges are:

• Alanine transaminase (ALT): 0 to 45 IU/L.
• Aspartate transaminase (AST): 0 to 35 IU/L.
• Alkaline phosphatase (ALP): 30 to 120 IU/L.
• Gamma-glutamyltransferase (GGT): 0 to 30 IU/L.
• Bilirubin: 2 to 17 micromoles/L.
• Prothrombin time (PT): 10.9 to 12.5 seconds.
• Albumin: 40 to 60 g/L.
• Total proteins: 3 to 8.0 g/dL.

What do high AST and ALT mean?

Elevated AST and ALT levels may indicate liver injury. These are the enzymes that are most commonly released into your bloodstream when your liver is stressed. If both are elevated equally, it indicates a nonalcoholic type of injury, which may include infection or other toxins. When AST is elevated twice as high as ALT, it indicates alcohol-induced injury.

What can a liver function test diagnose?

These blood tests may not be enough to decisively diagnose a specific liver disease, but they can point your healthcare provider in the right direction and help rule out other possibilities. You might need further tests, such as imaging tests, a liver biopsy or blood tests for specific viruses to help make your final diagnosis. Possible diagnoses may include:

• Fatty liver disease.
• Toxic hepatitis.
• Autoimmune hepatitis.
• Viral hepatitis (A, B or C).
• Hemochromatosis.
• Wilson’s disease.
• Alpha-1 antitrypsin deficiency.
• Primary biliary cholangitis (PBC).
• Cirrhosis.
• Liver cancer.

A note from Cleveland Clinic

A liver function test is one of the simplest ways you and your healthcare provider can check on your liver. Whether they’re looking for liver disease or they just want to test the effects of a medication or treatment, it only takes a small sample of your blood to yield a lot of information. Liver function tests may not provide enough information in themselves to make a diagnosis. But what you learn from the test will help guide the next steps.