Liver Function Tests: Purpose and Procedure
Liver function tests are blood tests that can be used to monitor the health of your liver. Ask the doctor what you need to do to prepare. In some cases you may need to avoid food or certain medications before the test.
Liver function tests, also known as liver chemistries, help determine the health of your liver by measuring the levels of proteins, liver enzymes, and bilirubin in your blood. They can also monitor the progression or treatment of an existing disease.
Depending on the test, either higher- or lower-than-typical levels of these enzymes or proteins can indicate a problem with your liver.
Some of the reasons liver function tests may be performed include screening for diseases such as hepatitis, monitoring the side effects of your medications, and examining the severity of liver disease.
In this article, we take a look at when you might need a liver function test, the different types of tests used, and how to interpret results.
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A liver function test is often recommended in the following situations:
- to check for damage from liver infections, such as hepatitis B and hepatitis C, especially if it’s suspected you were exposed to a virus that causes hepatitis
- to monitor the side effects of certain medications because some medications are known to affect the liver, including:
- NSAIDs
- statins
- antibiotics
- antiseizure medications
- tuberculosis drugs
- high triglycerides
- diabetes
- high blood pressure
- anemia
Certain tests can reflect different aspects of liver function. For example, elevated alanine transaminase and aspartate transaminase disproportional to bilirubin and alkaline phosphatase levels often indicates liver disease.
Liver function tests are used to measure specific enzymes and proteins in your blood.
Having atypical results on any of these liver tests usually requires a follow-up to determine the cause of the atypical characteristics. Even mildly elevated results can be associated with liver disease.
Common liver function tests include:
Alanine transaminase (ALT) test
Alanine transaminase (ALT) is used by your body to metabolize protein. If the liver is damaged or not functioning properly, ALT can be released into the blood. This causes ALT levels to increase. A higher result than what’s typical on this test can be a sign of liver damage.
It’s estimated that about 10 percent of people in the United States have elevated ALT levels.
Aspartate aminotransferase (AST) test
Aspartate aminotransferase (AST) is an enzyme found in several parts of your body, including your:
When the liver is damaged, AST can be released into the bloodstream. A high result on an AST test might indicate a problem with the liver or muscles.
Since AST levels aren’t as specific of a marker for liver damage as ALT, it’s usually measured together with ALT to check for liver problems. For example, a high AST:ALT ratio may indicate alcoholic liver disease .
Alkaline phosphatase (ALP) test
Alkaline phosphatase (ALP) is an enzyme found in your bones, bile ducts, and liver. An ALP test is typically ordered in combination with several other tests. An ALP test can be used to evaluate the bile duct system of the liver.
Albumin test
Albumin is the main protein made by your liver. It performs many important bodily functions.
For example, albumin nourishes your tissues and transports hormones, vitamins, and other substances throughout your body. An albumin test measures how well your liver is making this particular protein.
Bilirubin test
Bilirubin is a waste product from the breakdown of red blood cells. It’s ordinarily processed by the liver. It passes through the liver before being excreted through your stool.
A damaged liver can’t properly process bilirubin. This leads to an atypically high level of bilirubin in the blood. Certain inherited diseases can raise bilirubin levels, even when liver function works as expected.
The following table shows what liver function tests may indicate in terms of higher or lower results than typical. Following any liver function test, you should have a discussion with your doctor about your test results and what they mean for you.
Liver test Indications Typical and atypical ranges ALT test A higher result than typical on this test can be a sign of liver damage. Problems with the liver can make a person very sick and can even be life threatening. Approximately 4.5 million adults in the United States have chronic liver disease.
Symptoms of a liver disorder include:
- weakness
- fatigue or loss of energy
- weight loss
- jaundice (yellow skin and eyes)
- fluid collection in the abdomen, known as ascites
- discolored bodily discharge (dark urine or light stools)
- nausea
- vomiting
- diarrhea
- abdominal pain
- atypical bruising or bleeding
Your doctor may order a liver function test if you’re experiencing symptoms of a liver disorder.
Liver function tests can also monitor the progression or treatment of a disease and test for the side effects of certain medications.
Your doctor will give you complete instructions on how to prepare for the blood sample portion of the test.
Certain medications and foods may affect levels of these enzymes and proteins in your blood. Your doctor may ask you to avoid some types of medications, or they may ask you to avoid eating anything for a period of time before the test. Be sure to continue drinking water prior to the test.
You may want to wear a shirt with sleeves that can easily be rolled up to make it easier for the medical expert to collect the blood sample.
You may have your blood drawn in a hospital or at a specialized testing facility. To administer the test:
- The healthcare technician will clean your skin before the test to decrease the likelihood that any microorganisms on your skin will cause an infection.
- They’ll likely wrap an elastic strap on your arm. This will help your veins become more visible. They’ll then use a needle to draw samples of blood from your arm.
- After the draw, the technician will place some gauze and a bandage over the puncture site. Your blood sample will be sent to a laboratory for testing.
Potential risks of a liver function test
Blood draws are routine procedures and rarely cause any serious side effects. However, the risks of giving a blood sample can include:
- bleeding under the skin, or hematoma
- excessive bleeding
- fainting
- infection
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After the test, you can usually resume everyday activities. However, if you feel faint or lightheaded during the blood draw, you should rest before you leave the testing facility.
The results of these tests may not tell your doctor exactly which condition you have or the degree of liver damage, but they might help your doctor determine the next steps. Your doctor will call you with the results or discuss them with you at a follow-up appointment.
In general, if your results indicate a problem with your liver function, your doctor will review your medications and your past medical history to help determine the cause.
If you drink alcohol frequently, then you’ll need to stop drinking it. If your doctor identifies that a medication is causing the elevated liver enzymes, they’ll advise you to stop the medication.
Other diagnostic tests
Your doctor may decide to test you for hepatitis, other infections, or other diseases that can affect the liver. They may also choose to do imaging tests, like an ultrasound or CT scan.
In addition, they may recommend a liver biopsy to evaluate the liver for fibrosis, fatty liver disease, or other liver conditions.
Liver function tests are blood tests used to help determine the health of your liver. Changes in certain levels of proteins or enzymes can alert doctors of potential problems such as liver cancer, fatty liver disease, or hepatitis.
Liver function tests can also help determine if certain medications are damaging your liver or help you monitor the progression of liver disease.
After you get a liver function test, your doctor can help you interpret the results and discuss what the results mean for you. If they suspect you have liver disease, you may need to undergo other tests such as imaging or a liver biopsy.
Last medically reviewed on January 7, 2022
