Aspartate Aminotransferase

Aspartate Amino transferase

Synonym - Specimen - Reference Value - Method - Description -Indications - Interpretation 

Synonym             :

Serum glutamic-oxaloacetic transaminase      ,AST ,SGOT , GOT 

Specimen           : Serum 

Reference Value : 15 -35 IU / L

Method               : Spectrophotometry, enzymatic at 37 C 

Description 

Aspartate aminotransferase (AST ) is an enzymatic that catalyzes the reversible transfer of an amino group between aspartate and alfa-ketoglutaric acid . It was formerly known as serum glutamic - oxaloacetic transaminase (SGOT ) .AST  is not organ specific , it exists in large amounts in liver , skeletal muscle , brain , red cells and heart . Serum AST  rises when there is cellular damage to the tissues where the enzyme is found . Erythrocytes contain enough to raise levels when hemolysis occurs . It is located in the cytoplasm and mitochondria as different iso-enzymes .

Elevations in the cytoplasmic AST  iso-enzyme requires only mild hepatocellular injury , whereas release of the mitochondria iso-enzyme requires ( and indicates ) more server cellular injury . AST values greater than 500 U / L are usually associated with hepatitis and other hepatocellular  diseases in acute phase . AST levels are very elevated at birth and decrease with age . 

Note: Measurement of AST  in evaluation of myocardial infraction has been replaced by more sensetive tests  , such as creatine kinase - MB fraction ( CK-MB) and troponin .The enzyme half life is 5 -12 hours . 

Indications

- AST is useful as indicator of liver and/or muscle injury 

- Monitor response to therapy with potentially hepatotoxic

Interpretation 

Significantly increased in

( greater than five times normal levels ) 

- Acute hepatitis 

- Acute hepatocellular diseases

Serum activity of the AST increases when sufficient number of hepatocytes experience increased membrane permeability or destruction . Serm levels depend on both the number of cells  affected and the severity of injury to individual cells . Primary  hepatic disorders with high AST include inflammation due to viral , bacterial , fungal and immune mediated causes    . Inflammation can be suppurative or non-suppurative . Intoxications: Drugs , chemicals m plants . These can cause very high enzyme activity if associated with  diffuse necrosis . 

- Shock  and acute pancreatitis ( cause secondary hepatic disorders ) 

- Infectious myositis

Note that as AST has longer half life than CK ,increases in AST persist for longer than increases in CK .  Therefore , in chronic muscle disease , AST may be elevated whilst CK levels may be normal . When there is active muscle disease , both CK and AST are elevated ( and CK will decline more rapidly as injury resolves ). 

- Moderately increased in 

( three to five times normal levels )

- Biliary tract obstruction ( result in secondary hepatocellular injury as accumulated bile acids are toxic to cells ) 

- Cardiac arrhythmias 

- Chronic hepatitis 

- Congestive heart failure 

- Dermatomyositis 

- Liver tumors ( Variable increases are possible depending on the extent of active hepatocellular injury ) . 

- Muscular dystrophy 

Slightly increased in 

( two to three times normal ) 

- Cerebrovascular accident 

- Cirrhosis , fatty liver ( due to reduced number of cells and minimal active injury ) 

- Hemolytic anemia 

- pericarditis 

- Decrease in : pyridoxine ( Vitamin B6 ) deficiency .