Wednesday, June 27, 2012

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Aminotransferases (Transaminases)


Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are measured by the serum glutamic-oxaloacetic  transaminase (SGOT) and serum glutamic-pyruvic transaminase (SGPT) respectively. They are important markers of hepatocellular injury.

Normal values:  (varies from lab to lab but on average)
ALT : 7-41 U/L
AST: 12-38 U/L

AST can be found in various tissues like cardiac/skeletal muscles, kidney, brain and liver.
ALT is limited primarily to the liver and thus ALT is a more specific reflection of hepatocellular disease than AST.

The highest elevations of both enzymes are seen in viral, toxin-induced and ischemic hepatitis. On the other hand, alcoholic hepatitis usually gives a lower raise of around < 300 U/L. 

AST/ALT ratio is a useful indicator.
a) A ratio of > 2 is highly suggestive of alcohol-induced hepatic injury.
b) A ratio of > 1 and cirrhosis is often seen in patients of chronic hepatitis B infections.
c) A ratio of < 1 is commonly seen in acute/chronic viral hepatitis or in extra hepatic biliary obstruction.

Elevated AST or ALT are not definitive predictive indices of histologic findings. Instead serial measurements may reflect the extent of damage and give information about the progression of the disease.

A decrease in previously elevated enzymes does not always indicate recovery. In cases of fulminant hepatic failure, a decrease in the level of enzymes indicates that there is a low hepatic reserve after overwhelming hepatocyte necrosis. i.e. there is so much damage that the remaining normal hepatocytes are releasing only a small amount of the enzymes upon insult.
False low levels are seen in patients with uremia and chronic renal failure undergoing dialysis. False elevation is seen in patients treated with erythromycin.

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