What is Liver Function Testing?
Liver function tests are blood tests used to help diagnose and monitor liver disease or damage. The tests measure the levels of certain enzymes and proteins in your blood.
Some of these tests measure how well the liver is performing its normal functions of producing protein and clearing bilirubin, a blood waste product. Other liver function tests measure enzymes that liver cells release in response to damage or disease.
Abnormal liver function test results don’t always indicate liver disease. Your doctor will explain your results and what they mean.
Why is Liver Function Testing performed?
Liver function tests can be used to:
- Screen for liver infections, such as hepatitis
- Monitor the progression of a disease, such as viral or alcoholic hepatitis, and determine how well a treatment is working
- Measure the severity of a disease, particularly scarring of the liver (cirrhosis)
- Monitor possible side effects of medications
Liver function tests check the levels of certain enzymes and proteins in your blood. Levels that are higher or lower than normal can indicate liver problems. Some common liver function tests include:
- Alanine transaminase (ALT). ALT is an enzyme found in the liver that helps your body metabolize protein. When the liver is damaged, ALT is released into the bloodstream and levels increase.
- Aspartate transaminase (AST). AST is an enzyme that helps metabolize alanine, an amino acid. Like ALT, AST is normally present in blood at low levels. An increase in AST levels may indicate liver damage or disease or muscle damage.
- Alkaline phosphatase (ALP). ALP is an enzyme in the liver, bile ducts and bone. Higher-than-normal levels of ALP may indicate liver damage or disease, such as a blocked bile duct, or certain bone diseases.
- Albumin and total protein. Albumin is one of several proteins made in the liver. Your body needs these proteins to fight infections and to perform other functions. Lower-than-normal levels of albumin and total protein might indicate liver damage or disease.
- Bilirubin is a substance produced during the normal breakdown of red blood cells. Bilirubin passes through the liver and is excreted in stool. Elevated levels of bilirubin (jaundice) might indicate liver damage or disease or certain types of anemia.
- Gamma-glutamyltransferase (GGT). GGT is an enzyme in the blood. Higher-than-normal levels may indicate liver or bile duct damage.
- L-lactate dehydrogenase (LD). LD is an enzyme found in the liver. Elevated levels may indicate liver damage but can be elevated in many other disorders.
- Prothrombin time (PT). PT is the time it takes your blood to clot. Increased PT may indicate liver damage but can also be elevated if you’re taking certain blood-thinning drugs, such as warfarin.
What should I know before receiving Liver Function Testing?
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
How to prepare for Liver Function Testing?
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.
What happens during Liver Function Testing?
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 health care provider will place some gauze and a bandage over the puncture site. Then they’ll send the blood sample to a laboratory for testing.
What happens after Liver Function Testing?
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.
If you have any questions about the Liver Function Testing, please consult with your doctor to better understand your instructions.
Explanation of results
What do my results mean?
Normal blood test results for typical liver function tests include:
- 7 to 55 units per liter (U/L)
- 8 to 48 U/L
- 45 to 115 U/L
- 3.5 to 5.0 grams per deciliter (g/dL)
- Total protein. 6.3 to 7.9 g/dL
- 0.1 to 1.2 milligrams per deciliter (mg/dL)
- 9 to 48 U/L
- 122 to 222 U/L
- 9.5 to 13.8 seconds
These results are typical for adult men. Normal results vary from laboratory to laboratory and might be slightly different for women and children.
Your doctor will use these results to help diagnose your condition or determine treatment you might need. If you already have liver disease, liver function tests can help determine how your disease is progressing and if you’re responding to treatment.
Depending on the laboratory and hospital, the normal range for Liver Function Testing may vary. Please discuss with your doctor any questions you may have about your test results.
Hello Health Group does not provide medical advice, diagnosis or treatment.
Liver function tests. https://www.mayoclinic.org/tests-procedures/liver-function-tests/about/pac-20394595. Accessed October 19, 2018.
Liver Function Tests. https://www.healthline.com/health/liver-function-tests. Accessed October 19, 2018.
Review Date: November 4, 2018 | Last Modified: November 4, 2018