Liver tests are blood tests that represent a noninvasive way to screen for the presence of liver disease (for example, hepatitis in donated blood) and to measure the severity and progress of liver disease as well as the response to treatment.
Laboratory tests are generally effective for the following:
Detecting liver inflammation, damage, or dysfunction
Assessing the severity of liver injury
Monitoring the course of liver diseases and a person's response to treatment
Refining the diagnosis
Liver tests are done on blood samples and measure the levels of enzymes and other substances produced by the liver. These substances include
Levels of some of these substances measure the presence and degree of liver inflammation (for example, ALT, AST). Levels of other substances measure how well the liver performs its normal functions of making proteins and secreting bile (for example, albumin, bilirubin). What constitutes a normal value for many of these tests can be found in table Blood Tests. However, some of these values can be higher than normal in people with disorders not related to the liver.
One test of liver function is the prothrombin time (PT), which is used to calculate the international normalized ratio (INR). Both the PT and the INR are measures of the time needed for blood to clot (the liver synthesizes some proteins necessary for blood clotting, called blood clotting factors). An abnormal PT or INR result can indicate an acute or chronic liver disorder. In both acute and chronic liver disorders, an increasing PT or INR typically indicates progression to liver failure.