Routine blood work often includes measurements for SGOT and SGPT, which are frequently grouped under the umbrella of “liver function tests.” Monitoring the levels of these two specific enzymes provides physicians with a window into the health of the liver and other major organs. Understanding what these tests measure and why they might be elevated is a common concern for many people reviewing their health reports.
Defining SGOT (AST) and SGPT (ALT)
SGOT (Serum Glutamic Oxaloacetic Transaminase) has been largely replaced by the modern term Aspartate Aminotransferase (AST). SGPT (Serum Glutamic Pyruvic Transaminase) is now generally referred to as Alanine Aminotransferase (ALT). Both AST and ALT belong to a class of enzymes called transaminases, which play a central role in amino acid metabolism.
The tests measure the concentration of these enzymes present in the bloodstream, which is typically quite low in a healthy individual. The shift in terminology reflects a preference for naming the enzymes based on the specific amino acids they process. The purpose of measuring them remains the same: to assess cellular integrity, particularly within the liver.
Enzyme Roles and Tissue Location
These transaminase enzymes are primarily responsible for converting amino acids into other substances the body can use for energy or protein synthesis. ALT (SGPT) catalyzes a reaction that is a significant part of the body’s machinery for metabolizing proteins and generating energy.
ALT is overwhelmingly concentrated in the cytoplasm of liver cells (hepatocytes), making it the more specific indicator for liver injury. AST (SGOT) is also found in the liver, but it is distributed more widely throughout the body. Significant amounts of AST are also located in the heart, skeletal muscles, kidneys, and red blood cells. This broader distribution means that an elevation in AST levels may stem from damage to tissues other than the liver.
Interpreting Elevated Levels
Elevated levels of AST and ALT in the blood indicate that cells containing these enzymes have been damaged or injured, causing their contents to leak out into the bloodstream. The degree of elevation often correlates with the extent of cellular damage. A mild increase is generally considered less than five times the upper limit of normal, while a severe elevation can be 15 times or more above the baseline.
Liver-related conditions are the most common cause of high levels, as the liver contains the highest concentration of both enzymes. Non-alcoholic fatty liver disease (NAFLD), viral hepatitis (A, B, or C), and alcohol-related liver disease are major causes of hepatocellular damage.
Physicians often look at the ratio of AST to ALT, sometimes called the De Ritis ratio, to help narrow the diagnostic possibilities. In most cases of acute liver injury, the ALT level is higher than the AST level, resulting in an AST/ALT ratio less than 1. However, an AST/ALT ratio of 2:1 or greater is highly suggestive of alcohol-related liver disease. A ratio greater than 1, where AST is higher than ALT, can also be seen in patients with cirrhosis or significant muscle damage.
Factors Affecting Test Results
While AST and ALT are primarily used to assess liver health, certain non-hepatic conditions and external factors can also cause them to spike. Because AST is present in muscle tissue, intense physical activity, such as a rigorous workout or weightlifting, can transiently elevate AST levels and sometimes ALT. This elevation is due to minor muscle injury and the subsequent release of the enzyme into circulation.
Certain prescription and over-the-counter medications can also induce liver injury, leading to elevated transaminases. Drug-induced liver injury is a well-recognized cause, and a patient’s medication list is always reviewed when elevated results are found. Furthermore, non-liver-specific issues, including thyroid disorders, celiac disease, and acute muscle injuries like rhabdomyolysis, can affect the results, particularly AST. These potential non-liver sources highlight why test results are always interpreted in the context of a person’s complete clinical picture and medical history.