ALT blood levels are checked by undergoing the alanine aminotransferase test to measure the level of the enzyme in the blood, notes WebMD. The enzyme is found mainly in the liver, but it is also available in the pancreas, heart, kidneys and muscles.
The alanine aminotransferase test is done to check for liver damage, determine if the patient has liver disease and determine if jaundice resulted from liver disease or a blood disorder, according to WebMD. The test also helps doctors learn the effects of drugs that can affect the liver. Low levels of ALT are available in the blood, but liver damage is present, the levels increase.