Tests of the Liver
There are many different liver tests and it is helpful to know what each of them means. Here, we explain common liver blood tests and how to understand your results:
Liver panel
A "liver panel" usually refers to several lab tests performed as a group. Depending on the provider or the laboratory, a liver panel usually includes tests for AST, ALT, bilirubin, and alkaline phosphatase.
Liver enzymes
Usually, the term "liver enzymes" refers to the AST and the ALT.
Liver function tests (LFTs)
The phrase "liver function tests" or "LFTs" is commonly used by patients and providers.
Liver function is best measured by the PT, INR and albumin. Therefore, if you are getting a PT, INR or albumin, these tests can determine how the liver is "functioning."
ALT (SGPT)
ALT, or alanine aminotransferase, is one of the two liver enzymes. It is sometimes known as serum glutamic-pyruvic transaminase, or SGPT. It is a protein made only by liver cells. When liver cells are damaged, ALT leaks out into the bloodstream and the level of ALT in the blood is elevated.
AST (SGOT)
AST, or aspartate aminotransferase, is one of the two liver enzymes. It is also known as serum glutamic-oxaloacetic transaminase, or SGOT. AST is a protein made by liver cells. When liver cells are damaged, AST leaks out into the bloodstream and the level of AST in the blood becomes elevated. AST is different from ALT because AST is found in parts of the body other than the liver—including the heart, kidneys, muscles, and brain. When cells in any of those parts of the body are damaged, AST can be elevated.
Bilirubin
Bilirubin is a yellowish substance that is created by the breakdown (destruction) of hemoglobin, a major component of red blood cells. As red blood cells age, they are broken down naturally in the body. Bilirubin is released from the destroyed red blood cells and passed on to the liver. The liver releases the bilirubin in fluid called bile. If the liver is not functioning correctly, the bilirubin will not be properly released. Therefore, if the bilirubin level is higher than expected, it may mean that the liver is not functioning correctly.
Albumin
Albumin is a protein made by the liver. Albumin prevents fluid from leaking out of blood vessels into tissues. Albumin levels can go up and down slightly. Very low albumin levels can cause symptoms of edema, or fluid accumulation, in the abdomen (called ascites) or in the leg (called edema).
Prothrombin time (PT)
Prothrombin is a protein made by the liver. Prothrombin helps blood to clot. The "prothrombin time" (PT) is one way of measuring how long it takes blood to form a clot, and it is measured in seconds (such as 13.2 seconds). A normal PT indicates that a normal amount of blood-clotting protein is available.
When the PT is high, it takes longer for the blood to clot (17 seconds, for example). This usually happens because the liver is not making the right amount of blood clotting proteins, so the clotting process takes longer. A high PT usually means that there is serious liver damage or cirrhosis. A high PT may indicate there is a higher risk for internal bleeding from the upper part of the GI tract (esophagus, stomach).
Alkaline phosphatase
Alkaline phosphatase (often shortened to alk phos) is an enzyme made in liver cells and bile ducts. The alk phos level is a common test that is usually included when liver tests are performed as a group.
A high alk phos level does not reflect liver damage or inflammation. A high alk phos level occurs when there is a blockage of flow in the biliary tract or a buildup of pressure in the liver--often caused by a gallstone or scarring in the bile ducts.
INR
International normalized ratio (INR) is blood-clotting test. It is a test used to measure how quickly your blood forms a clot, compared with normal clotting time.
A normal INR is 1.0. Each increase of 0.1 means the blood is slightly thinner (it takes longer to clot). INR is related to the prothrombin time (PT). If there is serious liver disease and cirrhosis, the liver may not produce the proper amount of proteins and then the blood is not able to clot as it should. When your provider is evaluating the function of your liver, a high INR usually means that the liver is not working as well as it could because it is not making the blood clot normally.
Platelets
Platelets are cells that help the blood to form clots. The platelet number or "platelet count" in the blood is measured as part of the complete blood count (CBC).
Platelet counts in a patient who has cirrhosis are often low. But low platelet counts can also come from other causes, including certain medications. When the platelet count is extremely reduced, this condition is known as "thrombocytopenia." If a platelet count is too low, the patient cannot make normal clots and may bruise or bleed more easily.
Total protein
Total protein level is a measure of a number of different proteins in the blood. Total protein can be divided into the albumin and globulin fractions.
Low levels of total protein in the blood can occur because of impaired function of the liver.
Source: U.S. Department of Veterans Affairs