• Serum bilirubin test
Bilirubin is formed from the haem fragment of haemoglobin released by aged or damaged red blood cells. Liver, spleen and bone marrow are the sites of bilirubin production. Bilirubin formed in spleen and bone marrow is transported to the liver. In the liver it is converted into bilirubin conjugates – bilirubin mono- and di-glucuronides. Any liver disease affects the above systems, and hence bilirubin accumulates in serum leading to jaundice.
Bilirubin levels can be used to identify liver damage/disease or to monitor the progression of jaundice. Increased total and unconjugated bilirubin may be a result of hemolytic, sickle cell or pernicious anemias or a transfusion reaction. If conjugated bilirubin is elevated, there may be some kind of blockage of the liver or bile ducts, hepatitis, trauma to the liver, cirrhosis, a drug reaction, or long-term alcohol abuse. Inherited disorders that cause abnormal bilirubin metabolism (Gilbert’s, Rotor’s, Dubin-Johnson, Crigler-Najjar syndromes) may also cause increased levels. Low levels of bilirubin are not generally a concern and are not monitored.
• Alanine aminotransferase and aspartate aminotransferase tests
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels indicate the degree of inflammation. The aminotransferases are enzymes that are present in the liver cells (hepatocytes). They leak into the blood stream when the liver cells are damaged. These values are usually high in hepatitis – possibly twenty to fifty times higher than normal. The ALT value is more specific to the liver than the AST value. The AST value may also give an indication of muscle damage elsewhere in the body. Ratios of these enzymes can be helpful in detecting NASH and alcohol-related liver disease.
Normally, levels of ALT in the blood are low. Very high levels of ALT (more than 10 times the highest normal level) are usually due to acute hepatitis, often due to a virus infection. In acute hepatitis, ALT levels usually stay high for about 1–2 months but can take as long as 3–6 months to return to normal. Levels of ALT may also be markedly elevated as a result of exposure to drugs or other substances that are toxic to the liver as well as in conditions that cause decreased blood flow (ischemia) to the liver. ALT levels are usually not as high in chronic hepatitis, often less than four times the normal level. In this case, ALT levels often vary between normal and slightly increased, so doctors typically will order the test frequently to see if there is a pattern. Other causes of moderate increase in ALT include obstruction of bile ducts, cirrhosis (usually the result of chronic hepatitis or bile duct obstruction), and with tumors in the liver.
AST (SGOT) and ALT (SGPT) are sensitive indicators of liver damage or injury from different types of diseases. But it must be emphasized that higher-than-normal levels of these liver enzymes should not be automatically equated with liver disease. They may mean liver problems or they may not. For example, elevations of these enzymes can occur with muscle damage. The interpretation of elevated AST and ALT levels depends upon the entire clinical evaluation of an individual, and so it is best done by physicians experienced in evaluating liver disease and muscle disease.
• Alkaline phosphatase test
In conditions affecting the liver, damaged liver cells release increased amounts of ALP into the blood. This test is often used to detect blocked bile ducts because ALP is especially high in the edges of cells that join to form bile ducts. If one or more of them are obstructed, for example by a tumor, then blood levels of ALP will often be high.
High ALP usually means that either the liver has been damaged or a condition causing increased bone cell activity is present. If it is not clear from signs and symptoms or from other routine tests whether the high ALP is due to liver or bone, then a test for ALP isoenzymes may be necessary to distinguish between bone and liver ALP.
ALP results are usually evaluated along with other tests for liver disease. In some forms of liver disease, such as hepatitis, ALP is usually much less elevated than AST and ALT. When the bile ducts are blocked (usually by gallstones, scars from previous gallstones or surgery, or by cancers), ALP and bilirubin may be increased much more than AST or ALT. It may also be increased in liver cancer.
• Gamma-glutamyl Transpeptidase test
Gamma-glutamyl Transferase (GGT) levels may be used to determine the cause of an elevated alkaline phosphatase (ALP). Both ALP and GGT are elevated in disease of the bile ducts and in some liver diseases, but only ALP will be elevated in bone disease. If the GGT level is normal in a person with a high ALP, the cause is most likely bone disease.
The GGT test is sometimes used to help detect liver disease and bile duct obstructions. It is usually ordered in conjunction with or as follow up to other liver tests such as ALT, AST, ALP, and bilirubin. Increased levels of GGT levels may indicate in general that the liver is being damaged but does not specifically point to a condition that may be causing the injury. While elevated GGT levels may be caused by liver disease, they may also be caused by alcohol consumption and/or other conditions, such as congestive heart failure.
GGT can be used to screen for chronic alcohol abuse (it will be elevated in about 75% of chronic drinkers). Sometimes it may be used to monitor for alcohol use and/or abuse in people who are receiving treatment for alcoholism or alcoholic hepatitis.
• Clotting studies (prothrombin time)
Clotting studies, which may indicate liver disease, especially worsening chronic liver disease if the prothrombin time (clotting ability) is prolonged. Clotting is the thickening of blood, known as coagulation. The liver has a big role in the normal clotting of blood. When your liver is damaged your blood becomes too ‘thin’ and takes longer to clot. This may lead you to bruise more easily.