1 The blood tests most frequently used for liver disease are the aminotransferases (alanine aminotransferase or ALT and aspartate aminotransferase or AST). 2  Normal levels of ALT ranges from about 7-56 units/liter, and 10-40units/liters for AST. Many drugs may cause elevated AST, and ALT and some medications can cause severe damage (for example, acetaminophen [ Tylenol liver damage]). 2  Less common causes of abnormal AST and ALT levels are wide ranging (for example, toxins, and autoimmune diseases).