Alanine aminotransferase (ALT) and Aspartate aminotransferase (AST)
Alanine aminotranferease (ALT) and aspartate aminotransferase (AST) are enzymes located in liver cells that leak out into the general circulation when liver cells are injured. These two enzymes were previously known as the SGPT (serum glutamic-pyruvic transaminase) and the SGOT (serum glutaic-oxaloacetic transaminase). These two transaminase enzymes may be reported on lab slips with both their new names and previous names or by their newer names only. ALT and AST are present in highest concentrations in cells from the liver, heart, skeletal muscles, and red blood cells. Patients whose LFTs show a predominant rise in the transaminases have liver diseases that are characterized by hepatocellular damage.
ALT is found predominately in the liver, with lesser quantities found in the kidneys, heart, and skeletal muscle. As a result, the ALT is a more specific indicator of liver inflammation than the AST, as the AST may also be elevated in diseases affecting other organs, such as the heart or muscles. The AST is also elevated after a myocardial infarction, and during acute pancreatitis, acute hemolytic anemia, severe burns, acute renal disease, musculoskeletal diseases, and trauma. Because intramuscular (IM) injections cause muscle trauma that may release AST and ALT into the bloodstream, IM injections should be avoided before LFTs are done. If an IM injection must be given close to the time blood for LFTs is drawn, the nurse should indicate on the lab slip the time the injection is given. Many liver enzyme tests are also affected by medications. It is important to consult the laboratory manual for medications that should be considered in the interpretation of test results, and to indicate such medications on the lab slip.
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ALT is a more specific indicator of liver inflammation than the AST.
In acute liver injury, such as viral hepatitis, the ALT and AST may be as high as 1000U/L. In chronic hepatitis or cirrhosis of the liver, ALT and AST may be 10 to 100 times their normal values.