Your liver does all kinds of work that’s critical to your health. It helps break down food, clean your blood, make proteins, and store energy. If things go wrong with it, you might have a number of symptoms, from a yellow coloring of your skin to slurred speech. That’s when you might need a liver function test.
There’s actually not just one test. Your doctor will choose from several tests that check levels of different proteins and enzymes in your blood. Enzymes are special kinds of proteins that help speed up certain reactions in your body.
Some of the tests look for enzymes that you’d find in your blood only when your liver is damaged or has a disease. Others check to see whether that organ is working as expected.
When Would I Need One?
- Dark urine or light-colored stool
- No desire to eat
- Swelling in your belly
- Throwing up or feeling like you might
- Weakness or feeling very tired
- Yellowish eyes or skin (jaundice)
The test can also help your doctor see how bad an illness is getting or how well treatment is working.
Your doctor may order a liver function test if you’re more likely to have liver damage or disease. For example, if you’re:
Types of Tests
There are a number of liver function tests, with lots of complex names. You might hear your doctor or nurse mention some of the common ones, which include:
- Alanine transaminase (ALT) test. ALT is an enzyme that helps break down proteins and is found mainly in your liver. High levels in your blood could mean you have liver damage.
- Alkaline phosphatase (ALP) test. ALP is an enzyme you have in your liver, bile ducts, and bone. You might have high levels if you have liver damage or disease, a blocked bile duct, or bone disease.
- Albumin and total protein test. Your liver makes two main proteins: albumin and globulin. Low levels can mean damage or disease.
- Aspartate transaminase (AST) test. AST is another enzyme found in your liver. High blood levels could be a sign of damage or disease.
- Bilirubin test. Bilirubin is made when red blood cells break down. Usually, the liver cleans bilirubin out of your body. If you have high levels in your blood, a problem called jaundice, you may have liver damage.
- Gamma-glutamyltransferase (GGT) test. High levels of the GGT enzyme could point to liver or bile duct damage.
- L-lactate dehydrogenase (LD) test. LD is another enzyme that’s high when you have liver damage, but other conditions can raise its level, as well.
- Prothrombin time (PT) test. This test measures how long it takes your blood to clot. If it takes a long time, that could be a sign of liver damage. Medications that thin your blood, such as warfarin (Coumadin), can also lead to a longer PT.
How Do I Get Ready for the Test?
Because some foods and medicines can affect liver function test results, your doctor will likely ask you not to eat, drink, or take medicine for 10 to 12 hours before the test.
Make sure to tell your doctor about any medicines you’re taking, including over-the-counter medications and any herbal supplements.
What Happens During the Test?
The test is a basic blood draw. Your doctor uses a thin needle to take a small amount of blood, usually from your arm near your elbow. You’ll feel a pinch or stinging when the needle goes in. You may get some soreness or a bruise where the blood is taken, but that’s usually it.
Typically, these tests are done more than once over a few days or weeks. Your doctor can look at how levels change to be sure of your condition and how far along it is.
If you get your test at a clinic that has a lab on site, you can sometimes get results in a few hours. If not, it might take a few days.
What Do the Results Mean?
The results usually show the normal values along with your numbers. Keep in mind that what’s normal can vary with different labs. It also depends on whether you’re male or female.
If your results aren’t normal, you’ll likely get more tests. The liver function test alone can’t tell you for sure that you have a certain illness. Your doctor can help you understand what your results mean.