Are Liver Function Tests?
Liver function tests help
determine the health of your liver by measuring the levels of proteins, liver enzymes,
or bilirubin in your blood.
A liver function test is often given in the following situations:
- to screen for liver infections, such as
- 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
- to measure the degree of scarring (cirrhosis) on
- if you’re experiencing the symptoms of a liver
- if you’re planning on becoming pregnant
Many tests can be performed on the liver, but most of them don’t measure
the overall function of the liver. Commonly used tests to check liver function
are the alanine transaminase (ALT), aspartate aminotransferase (AST), albumin, and
bilirubin tests. The ALT and AST tests measure enzymes that your liver releases
in response to damage or disease. The albumin and bilirubin tests measure how
well the liver creates albumin,
a protein, and how well it disposes of bilirubin, a waste product of the blood.
Abnormal results on any of the liver function tests don’t
necessarily mean you have liver disease or damage. Talk to your doctor about
the results of your liver function test.
Are the Most Common Liver Function Tests?
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 is released
into the blood. This causes ALT levels to increase. A high result on this test can be a sign of liver damage.
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
specific for liver damage, it’s usually measured together with ALT to check for
liver problems. Your doctor may use an ALT-to-AST ratio to help with their
diagnosis. When the liver is damaged, AST is released into the bloodstream. A
high result on an AST test might indicate a problem with the liver or muscles.
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
damage, 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.
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
- 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 indicates that your liver isn’t
Bilirubin is a waste product ordinarily processed by the liver. The
breakdown of red blood cells creates this waste product. It passes through the
liver before being excreted through your stool.
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 indicates that the liver isn’t functioning properly.
Do I Need a Liver Function Test?
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 proteins, enzymes, and bile
- making factors that fight infection
- removing bacteria from your blood
- processing substances that could harm your body
- maintaining hormone balances
Problems with the liver can make a person very sick and can even
Symptoms of a liver disorder include:
- fatigue or loss of energy
- weight loss
- jaundice (yellow skin and eyes)
- symptoms of nephritic syndrome (swelling around
the eyes, belly, and legs)
- discolored bodily discharge (dark urine or light
- abdominal pain
Your doctor may order a liver function test if you’re
experiencing symptoms of a liver disorder or even if you’re planning to become
pregnant. The different liver function tests can also check for infection,
monitor the progression or treatment of a disease, and test for the side
effects of certain medications.
to Prepare for a Liver Function Test
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.
You may want to wear a shirt with sleeves that can easily be
rolled up to make it easier to collect the blood sample.
a Liver Function Test Is Performed
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 prevent any microorganisms on your skin from contaminating the
- They’ll likely wrap a cuff or some sort of
pressure device on your arm. This will help your veins become more visible. They
will use a needle to draw several 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 will send the
blood sample to a laboratory for testing.
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 include:
- bleeding under the skin, or hematoma
- excessive bleeding
a Liver Function Test
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.
When the results are available from the laboratory, your doctor
will review them. 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.