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Note: Measurement of AST in evaluation of myocardial infraction has been replaced by more sensetive tests , such as creatine kinase - MB fraction ( CK-MB) and troponin .The enzyme half life is 5 -12 hours .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