What are liver function tests?
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.
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
- to monitor the side effects of certain medications known to affect the liver
- if you already have a liver disease, to monitor the disease and how well a particular treatment is working
- if you’re experiencing the symptoms of a liver disorder
- if you have certain medical conditions such as high triglycerides, diabetes, high blood pressure, or anemia
- if you drink alcohol heavily
- if you have gallbladder disease
Many tests can be performed on the liver. Certain tests can reflect different aspects of liver function.
Commonly used tests to check liver abnormalities are tests checking:
- alanine transaminase (ALT)
- aspartate aminotransferase (AST)
- alkaline phosphatase (ALP)
The ALT and AST tests measure enzymes that your liver releases in response to damage or disease. The albumin test measures how well the liver creates albumin, while the bilirubin test measures how well it disposes of bilirubin. ALP can be used to evaluate the bile duct system of the liver.
Having abnormal results on any of these liver tests typically requires follow up to determine the cause of the abnormalities. Even mildly elevated results can be associated with liver disease. However, these enzymes can also be found in other places besides the liver.
Talk to your doctor about the results of your liver function test and what they may mean for you.
Liver function tests are used to measure specific enzymes and proteins in your blood.
Depending on the test, either higher- or lower-than-normal levels of these enzymes or proteins can indicate a problem with your liver.
Some 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 than normal result on this test can be a sign of liver damage.
According to the American College of Gastroenterology, an ALT above 25 IU/L (international units per liter) in females and 33 IU/L in males typically requires further testing and evaluation.
Aspartate aminotransferase (AST) test
Aspartate aminotransferase (AST) is an enzyme found in several parts of your body, including the heart, liver, and muscles. Since AST levels aren’t as specific for liver damage as ALT, it’s usually measured together with ALT to check for liver problems.
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.
The normal range for AST is typically up to 40 IU/L in adults and may be higher in infants and young children.
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.
High levels of ALP may indicate liver inflammation, blockage of the bile ducts, or a bone disease.
Children and adolescents may have elevated levels of ALP because their bones are growing. Pregnancy can also raise ALP levels. The normal range for ALP is typically up to 120 U/L in adults.
Albumin is the main protein made by your liver. It performs many important bodily functions. For example, albumin:
- stops fluid from leaking out of your blood vessels
- nourishes your tissues
- transports hormones, vitamins, and other substances throughout your body
An albumin test measures how well your liver is making this particular protein. A low result on this test can indicate that your liver isn’t functioning properly.
The normal range for albumin is 3.5–5.0 grams per deciliter (g/dL). However, low albumin can also be a result of poor nutrition, kidney disease, infection, and inflammation.
A damaged liver can’t properly process bilirubin. This leads to an abnormally high level of bilirubin in the blood. A high result on the bilirubin test may indicate that the liver isn’t functioning properly.
The normal range for total bilirubin is typically 0.1–1.2 milligrams per deciliter (mg/dL). There are certain inherited diseases that raise bilirubin levels, but the liver function is normal.
Liver tests can help determine if your liver is working correctly. The liver performs a number of vital bodily functions, such as:
- removing contaminants from your blood
- converting nutrients from the foods you eat
- storing minerals and vitamins
- regulating blood clotting
- producing cholesterol, proteins, enzymes, and bile
- making factors that fight infection
- removing bacteria from your blood
- processing substances that could harm your body
- maintaining hormone balances
- regulating blood sugar levels
Problems with the liver can make a person very sick and can even be life-threatening.
Symptoms of a liver disorder include:
- 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)
- abdominal pain
- abnormal bruising or bleeding
Your doctor may order a liver function test if you’re experiencing symptoms of a liver disorder. The different 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 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 provider 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 use a needle to draw samples of blood from your arm.
- After the draw, the healthcare provider will place some gauze and a bandage over the puncture site. Then they’ll send the blood sample to a laboratory for testing.
Blood draws are routine procedures and rarely cause any serious side effects. However, the risks of giving a blood sample can include:
After the test, you can usually leave and go about your life as usual. 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 any 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 heavily, then you’ll need to stop drinking. If your doctor identifies that a medication is causing the elevated liver enzymes, then they’ll advise you to stop the medication.
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, like an ultrasound or CT scan. They may recommend a liver biopsy to evaluate the liver for fibrosis, fatty liver disease, or other liver conditions.