Liver Blood Test
Siamak T. Nabili, MD, MPH
Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
- What are the basic functions of the liver?
- What are common liver blood tests?
- What are the aminotransferases?
- Normally, where are the aminotransferases?
- What are normal levels of AST and ALT?
- What do elevated liver tests (AST and ALT) mean?
- Does AST and ALT measurements indicate liver function?
- Which blood tests are done to detect liver function?
- What are some common reasons for abnormal liver tests?
- What medications can cause abnormal aminotransferase levels?
- What conditions can cause very high aminotransferase levels?
- What are some of the less common causes of elevated liver blood tests?
- How are healthy people evaluated for mild to moderate rises in aminotransferase levels?
- How about monitoring liver blood tests?
- What about the other liver enzymes?
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What are the basic functions of the liver?
The liver, located in the right upper portion of the abdominal cavity just beneath the right side of the rib cage, has many vital functions. Briefly, some of these functions are:
- Detoxification of blood
- Production of important clotting factor and other important proteins
- Metabolizing (processing) medications and nutrients
- Processing of waste products of hemoglobin
- Storing of vitamins, fat, cholesterol, and bile
- Production of glucose
What are common liver blood tests?
Liver blood tests are some of the most commonly performed blood tests. These tests can assess liver functions or liver injury. An initial step in detecting liver damage is a simple blood test to determine the presence of certain liver enzymes (proteins) in the blood. Under normal circumstances, these enzymes reside within the cells of the liver. But when the liver is injured for any reason, these enzymes are spilled into the blood stream. Enzymes are proteins that are present throughout the body, each with a unique function. Enzymes help to speed up (catalyze) routine and necessary chemical reactions in the body.
Among the most sensitive and widely used liver enzymes are the aminotransferases. They include aspartate aminotransferase (AST or SGOT) and alanine aminotransferase (ALT or SGPT). These enzymes are normally contained within liver cells. If the liver is injured or damaged, the liver cells spill these enzymes into the blood, raising the enzyme levels in the blood and signaling liver disease.
Other blood tests pertaining to the liver are measurements of some of the other enzymes found the liver. In addition to AST and ALT, alkaline phosphatase, 5' nucleotidase, and gamma-glutamyl transpeptidase (GGT) are other enzymes located in the liver. The focus of this article is mainly on the most common liver enzymes, AST and ALT.
What are the aminotransferases?
The aminotransferases catalyze chemical reactions in which an amino group from one amino acid (amino acids are building blocks of proteins) is transferred from a donor molecule to a recipient molecule. Hence, the names "aminotransferases."
Medical terms can sometimes be confusing, as is the case with these enzymes.
- Another name for aminotransferase is
transaminase.
- The enzyme aspartate aminotransferase (AST) is also known as serum
glutamic oxaloacetic transaminase (SGOT).
- Alanine aminotransferase (ALT) is also known as serum glutamic pyruvic transaminase (SGPT).
To put matters briefly, AST = SGOT and ALT = SGPT.
Normally, where are the aminotransferases?
AST (SGOT) is normally found in a variety of tissues including liver, heart, muscle, kidney, and brain. It is released into the serum when any one of these tissues is damaged. For example, its level in serum rises in heart attacks or with muscle disorders. It is therefore, not a highly specific indicator of liver injury as it can occur from other injured tissues.
ALT (SGPT) is, by contrast, normally found largely in the liver. This is not to say that it is exclusively located in liver, but that is where it is most concentrated. It is released into the bloodstream as the result of liver injury. Thus, it serves as a fairly specific indicator of liver status.
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