Lab tests are often used to confirm a diagnosis (along with history and physical exam) and to monitor disease and treatment. Many lab tests measure enzyme levels. This is because when tissues are damaged cells die and enzymes are released into the blood. Levels of these enzymes are tested for, and these tests are often referred to as liver function tests. An organ system as complex as the liver will often be evaluated using several tests. This is because more than one system may release the same enzyme when the tissue is damaged. Therefore, when determining how the liver is working, and what may be causing problems, there are several tests that may be done together and are collectively known as "liver function tests."
- Common liver function tests are AST (aspartate transaminase), also known as SGOT (serum glutamic-oxaloacetic transaminase), and ALT, (alanine transaminase) also known as SGPT (serum glutamic-pyruvic transaminase). Together the AST and ALT will tell if there is liver tissue damage or inflammation. ALT is more specific to liver damage than AST. It is not unusual to find mild elevations (up to 2 times normal) of AST and ALT. Levels of AST and ALT more than two times normal, however, are generally considered to be significant and require further investigation.
- Alkaline phosphatase is another test that may be done if there is concern about the liver, and may indicate obstruction of the bile drainage system.
- LDH (lactic acid dehydrogenase) is a non-specific enzyme that may be increased when the liver is compromised.
- GGT (gamma glutamyl transferase) is an enzyme whose levels are measured to screen for liver disease and to monitor cirrhosis (hardening or scarring of the liver, especially from alcoholism). It is also helpful in diagnosing blockage of ducts that drain bile from the liver to the intestines.
- In addition, bilirubin is also used to evaluate the liver. Bilirubin is not an enzyme. It is a product of the breakdown of red blood cells (RBCs) by the liver. Levels of bilirubin may increase if the liver is not functioning or there is an excess of RBCs destroyed. Levels may also increase if there is a blockage of the ducts that carry bile from the liver. Urine tests for urobilinogen, a by-product of bilirubin metabolism in the digestive tract, can be helpful in determining if the symptoms are related to RBC destruction, liver disease or obstructed ducts.
- Viral hepatitis (A, B, C, and D) tests may be run to rule out a viral infection. These assays test for the presence of virus and antibodies in the blood. While the lab tests look at what is going on in cells, imaging studies look at the anatomy of organs.
- Ultrasound is used often to look for gallstones and inflammation of the liver and gall bladder. It can also detect masses that may be present in or around the liver. Similarly, CT (computerized tomography) gives a picture of the inside of the body.
- Doing a biopsy looks at the tissue itself, taking small pieces and examining them with a microscope.
It is the pattern of these tests' results that are used to determine how the liver is functioning, and what may be causing any problems. Don't hesitate to talk to your physician about any tests that are done, or to ask what they are being used for, (monitoring or diagnosing) what the results are, and how those results are being interpreted.