Liver enzyme blood tests are often performed as part of a more comprehensive test called a liver function test. The reason for this is because liver enzyme results only tell part of the story related to liver health and condition. Liver enzyme results measure enzymes the organ produces in response to damage or disease. Other testing also involved in the liver function test measures actual liver activity.
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While the measurement of liver enzymes is frequently part of a laboratory blood test known as the liver function test, testing for liver enzymes may also be performed independent of other testing. In many instances, it is the results of the liver enzyme tests in combination with other blood tests, such as albumin and bilirubin, that provide the most complete picture of liver health to the health care provider, notes MayoClinic.com. Some of the enzymes produced by the liver in instances of damage or disease are also produced by other parts of the body, so elevated levels of these enzymes must be assessed by the health care provider as to their meaning in each individual case.
There are two basic types of liver enzymes subject to measurement: transaminases and cholestatic liver enzymes, Dr. Melissa Palmer, internal medicine specialist and hepatologist, explains at the LiverDisease website. Aspartate aminotransferase, AST or SGOT, and alanine aminotransferase, ALT or SGPT, are the two transaminases. Gamma-glutamyl transferase, or GGT, and alkaline phosphatase, or AP, are the two cholestastic liver enzymes.
Liver damage or disease may be present even when liver enzyme levels are within normal limits or reference ranges. The Lab Tests Online website reports that liver function tests are not done on just one occasion to make a diagnosis of liver damage or disease. Many times, several liver function tests will be ordered over a period of time, which may be days or weeks. The health care provider will assess whether a pattern develops throughout the course of tests to better determine whether a liver disorder exists.
Determining the meaning of liver enzyme results and other results of a liver function test is complex. The results of liver enzyme tests on any given day may be affected by the time of day the blood sample is taken, medications taken, foods eaten and time most recent alcohol was consumed -- if any -- explains Dr. Palmer. Men tend to have higher levels of the transaminase enzymes than women, and African-American men tend to have higher AST levels than Caucasian men.
Considering the variety and complexity of factors affecting liver enzyme levels and the medical assessment required to make a determination of the meaning of those levels, liver enzyme levels need the evaluation skills of a trained health care provider for an accurate diagnosis.