Liver function tests are one of the blood tests that are most commonly performed to assess the function of the liver or injury caused to the liver. Liver damage is detected initially by performing a simple blood test that determines the level of various liver enzymes present in the blood. The most widely used liver enzymes that are sensitive to abnormalities in liver and are most commonly measured are the aminotransferases. The two aminotransferases that are checked are the alanine aminotransferase (ALT or SGPT) and aspartate aminotransferase (AST or SGOT). These liver enzymes form a major constituent of the liver cells. They are present in lesser concentration in the muscle cells. When the liver cells get damaged or injured, these enzymes seep into the blood stream, raising their blood levels. Hence raised blood levels of SGOT and SGPT signifies liver disease or injury.
The aminotransferases catalyze the chemical reactions involving the amino acids, where an amino group is transferred from the donor amino acid to the recipient molecule. Aminotransferases are also referred to as transaminases. Another name for AST is serum glutamic oxaloacetic transaminase (SGOT). Similarly another name for ALT is serum glutamic pyruvic transaminase (SGPT). Hence, AST is also referred to as SGOT and ALT is also referred to as SGPT.
SGOT is normally present in a number of tissues such as heart, liver, muscle, brain and kidney. It is released into the blood stream whenever any of these tissues gets damaged. For instance, blood AST level is increased in conditions of muscle injury and heart attacks. Hence, it is not highly specific liver tissue damage indicator as it can be elevated in conditions other than liver damage.
By contrast, SGPT is normally present in large concentrations in the liver. Hence, due to liver damage its level in the blood rises, thereby, serving as a specific indicator for liver injury.
To regard SGOT and SGPT as liver function tests is a misnomer that is commonly prevalent in the medical community as they do not reflect functioning of the liver. They only detect any type of liver injury or damage done to the liver due to any type of infection and inflammatory changes. The liver may keep functioning normally even in cases when both of these enzymes are highly raised.
The normal levels of SGOT is in between 5 and 40 units per liter of serum and the normal levels of SGPT in between 7 and 56 units per liter of serum.
The normal ranges of SGOT and SGPT may slightly differ depending on the protocols and techniques used to measure them by different laboratories. However, each laboratory routinely provides the normal reference ranges and prints it in the report.
SGOT and SGPT are highly sensitive markers of liver damage due to various diseases or injury. However, the fact is that higher than normal levels should not be automatically considered as indicative of liver damage. They may or may not imply liver disease. For instance, these enzymes are also elevated in cases of muscle damage. Hence, to interpret elevations in SGOT and SGPT, an individual must get an entire physical evaluation done by physicians who are experienced in evaluating liver and muscle problems.
Additionally, the precise levels of these enzymes and the intensity of liver disease and its prognosis or outlook do not correlate well. Hence, the precise blood levels of these enzymes cannot be utilized to determine the intensity or degree of liver illness and also to predict the outlook or prognosis of the disease. For instance, SGOT and SGPT are raised to high levels in individuals suffering from viral hepatitis A; they sometimes reach in the range of thousands of units/liter. However, most cases of acute viral hepatitis A recover completely with no signs of residual liver illness. Conversely, individuals developing chronic hepatitis C infection have minor elevations in their SGOT and SGPT levels, whereas, their liver is injured or damaged substantially by the infection even leading to scarring (cirrhosis) from ongoing liver infection and inflammation.