Information about Liver Blood Tests (enzymes)

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Liver Blood Test

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Medical Author: Siamak Nabili, MD, MPH
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

Liver...The Largest Gland in the Body!

Medical Author: Leslie J. Schoenfield, M.D., Ph.D.
Medical Editor: Jay W. Marks, M.D.

The liver is the largest solid organ in the body. I think a lot of people probably know that. But they may not know that it is also the largest gland in the body. You see, the liver is also considered a gland because, among its various functions, it makes and secretes bile. (Just for your reference, the stomach and intestine are large hollow organs. Glands are organs or parts of organs that make and secrete substances. And bile is a fluid that both aids in digestion and transports fats as well as waste products into the intestine.)

Actually, there are all sorts of glands in the body that make and secrete substances, including the pancreas (digestive enzymes), thyroid and other endocrine glands (hormones), gastric glands in the stomach (acid), and lymph glands or nodes (lymph). The liver is even larger, I think, than most mammary glands (milk).

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Introduction to liver blood test

An initial step in detecting liver damage is a simple blood test to determine the presence of certain liver enzymes 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 of these 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, the liver cells spill the enzymes into blood, raising the enzyme levels in the blood and signaling the liver damage.

What are the aminotransferases?

The aminotransferases catalyze chemical reactions in the cells in which an amino group (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); and
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 diversity of tissues including liver, heart, muscle, kidney, and brain. It is released into serum when any one of these tissues is damaged. For example, its level in serum rises with heart attacks and with muscle disorders. It is therefore, not a highly specific indicator of liver injury.

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. It therefore serves as a fairly specific indicator of liver status.