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Good News for Non-Responders to HCV Combination Therapy
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Purer, Less Costly Interferon for Hepatitis C and B Treatment
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New Technology May Help Treat Hepatitis
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Frequently Asked Questions about AST, ALT, GGTP, AP
Jeff Punch MD
Division of Transplantation
University of Michigan
What do these letters mean?
These letters are acronyms for enzymes - proteins inside of cells. AST for example
stands for aspartate amino transferase. This enzyme used to be called serum glutamic
oxalacetic transaminase (SGOT), hence the two names. ALT = amino alanine transferase,
GGTP= gamma glutamyl transpeptidase, and AP= alkaline phosphatase. Different cells
have different enzymes inside them, depending on the function of the cell. Liver
cells happen to have lots of AST, ALT, and GGTP inside them. When cells die or
are sick the enzymes leak out causing the blood level of these enzymes to rise,
which is a way of determining if the cells in question are sick. ALT is more specific
for liver disease than AST because AST is made in more places (e.g. heart, intestine,
muscle). So the AST will rise after a heart attack or bruised kidney. GGTP and
AP are said to be more specific for biliary disease since they are made in bile
duct cells. In liver disease caused by excess alcohol ingestion, the AST tends
to exceed the ALT, while the reverse is true to for viral hepatitis. However,
this particular generalization is often wrong.
Some points:
These tests have meaning, but they generally cannot be interpreted without
clinical information. They are probably most useful to track, or follow a particular
problem, but even then they often "bounce around" greatly.
These numbers are not linear. An AST that is 300 is not twice as bad as
150 (normal is less than 50). We are used to numbers like temperature and dollars.
If it is 94 degrees F outside, it is warmer than if it is 80 every time. And if
one has 94 dollars, one has more money than if one has 80. Liver enzyme values
don't behave this way. An AST of 94 and 80 are essentially the same to a liver
specialist.
These numbers do not always detect all liver disease. Some very patients
with severe advanced liver disease will have normal or nearly normal enzyme levels.
Are these numbers indicative of liver funtion?
Not really. Unfortunately, they are often called "liver function tests" or "LFT's",
but in actuality, they do not measure function per se.
Then how is liver function measured?
Other tests including albumin, bilirubin, and prothrombin time are more truely
measures of function, but clinical factors must be considered as well.
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