LIVER FUNCTION TESTS
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.
WHAT 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 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
- to measure the degree of scarring (cirrhosis) on the liver
- if you’re experiencing the symptoms of a liver disorder
- 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 transaminase (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.
WHY IT’S DONE?
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 warfari