Liver disease
Three types of tests are often used to detect liver disease; these tests either measure the levels of specific enzymes, bilirubin, or protein present in the test sample (usually a blood sample). Among the more common tests in these three categories are:
1. Enzymes: Enzymes are proteins that help cells do their work. When cells are injured, enzymes can leak into the blood at higher-than-normal levels. Three common enzymes used to detect liver disease are:
- Alanine aminotransferase (ALT) – an enzyme found mainly in the liver; the best test for detecting hepatitis
- Alkaline phosphatase (ALP) – an enzyme related to the bile ducts; often increased when they are blocked
- Aspartate aminotransferase (AST) – an enzyme found in the liver and a few other places, particularly the heart and other muscles
- Gamma glutamyl transferase (GGT) - an enzyme related to the bile ducts; increased in disease of the bile ducts, with alcohol abuse, or due to drugs such as phenytoin.
2. Bilirubin: A waste product made from old blood cells, it is a yellow compound that causes jaundice and dark urine when present in increased amounts. Two different tests of bilirubin are often used together, especially if a person has jaundice:
- Total bilirubin - measures all the bilirubin in the blood
- Conjugated bilirubin - measures a form made in the liver
3. Protein: One of the main functions of the liver is to make protein. Two important liver tests include:
- Albumin - measures the main protein made by the liver and tells how well the liver is making this protein
- Total Protein - measures albumin and all other proteins in blood, including antibodies made to help fight off infections (antibodies are not made in the liver)
Doctors often use these tests together to tell whether liver damage has occurred and how severe it is. When ordered together, these 8 tests are called liver function tests.
