The ALT blood test gauges the levels of alanine transaminase, an enzyme, in the blood. This enzyme is mostly located in the liver; however, trace amounts are also in the heart, kidneys, pancreas and muscles. The ALT blood test, formerly referred to as the serum glutamic pyruvic transaminase test, assesses how the liver is functioning.

This test determines if the liver is damaged or diseased. Livers release ALT into the bloodstream in very small amounts. Liver damage is the major cause of high levels of ALT in the bloodstream. The Alanine Aminotransferase blood test can detect the presence of a liver disease. Levels that are considered high are indicative of diseases like celiac disease, hepatitis, infectious mononucleosis and other diseases. The test is also used to monitor the effects of medication on the liver and to see if a case of jaundice is caused by liver disease.

While the ALT test is prescribed by doctors to check for the possibility of liver damage, it is often accompanied by a battery of tests that include the aspartate aminotransferase (AST), bilirubin and lactate dehydrogenase (LDH) test. These tests are included in the Basic Health Screening offered at the Health Testing Centers.