Liver Function Tests

Why This Test Is Done

Liver function tests are most often used to help:

• Find out if liver disease or damage could be causing certain symptoms
• Learn how serious liver disease is after it has been diagnosed
• Monitor liver disease over time and/or find out how well treatment is working
• Check for side effects of certain medicines that can affect the liver

How It Works

The most common liver function tests measure:

• Albumin, a protein made in the liver.
• Total protein. This test measures the total amount of protein in your blood, which includes albumin and globulins. These proteins are mainly made in your liver.
• ALP (alkaline phosphatase), ALT (alanine transaminase), AST(aspartate aminotransferase), and GGT (gamma-glutamyl transferase). These are enzymes that are mainly made in your liver. Enzymes are proteins that speed up certain chemical reactions in your body.
• Bilirubin, a waste product your body makes when it breaks down old red blood cells. Your liver removes most of the bilirubin from your body.
• Lactate dehydrogenase (LDH), an enzyme found in most of the tissues in your body, but some of the largest amounts are found in your liver.
• Prothrombin time (PT), how long it takes your blood to clot. Prothrombin is a protein involved in blood clotting. It's made in your liver.

Some of these tests can show how well your liver is working and others can show whether your liver may be damaged by liver disease or injury. But liver function tests alone usually can't diagnose specific diseases. So, if your results are abnormal, you'll usually need other tests to find the exact cause.

Preparing For The Test

Your healthcare provider will tell you how to prepare for your test. You will probably need to fast (not eat or drink) for 10-12 hours before the test. 

Certain medicines can affect your test results, so be sure to tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

What Happens During The Test

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

After The Test

Understanding abnormal liver function test results is often complicated. So, it's best to ask your provider to explain what your results say about your health.

If any of your liver function test results are abnormal, your provider will compare the results of all the substances that were measured. This is done to look for certain patterns of normal and abnormal results that suggest different types of liver conditions.

In general, the results of your liver function tests can tell you if:

• Your liver is inflamed, which means you have hepatitis.
• You have hepatitis from drinking alcohol or other causes, such as infection.
• Your liver isn't working well and how weak it has become.
• You have a problem with your bile ducts. Bile is a digestive "juice" that your liver makes. Bile ducts are the tubes that carry bile through your liver and out of your liver.
• Medicines are harming your liver and how serious the damage is.

Abnormal results don't always mean you have a problem with your liver. Other conditions can cause high or low levels of certain substances that these tests measure. For example, high levels of ALP can be a sign of bone disease or liver disease. So, your provider will also consider your symptoms, medical history, risk for liver disease, and any medicines you take.

If you have been ill recently, certain types of abnormal results may be temporary. In this case, your provider may repeat the tests later to see if your results return to normal.

Risks

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.