Aspartate aminotransferase (glutamate oxalacetate transaminase) belongs to the transaminases, which catalyze the interconversion of amino acids and α‑ketoacids by transfer of amino groups. Aspartate aminotransferase is commonly found in human tissue. Although heart muscle is found to have the most activity of the enzyme, significant activity has also been seen in the brain, liver, gastric mucosa, adipose tissue, skeletal muscle, and kidneys.
Two isoenzymes of AST have been detected, cytoplasmic and mitochondrial. Only the cytoplasmic isoenzyme occurs in normal serum, while the mitochondrial, together with the cytoplasmic isoenzyme, has been detected in the serum of patients with coronary and hepatobiliary disease.
Measurement of AST is indicated in the diagnosis, differentiation and monitoring of hepatobiliary disease, myocardial infarction and skeletal muscle damage. AST measurement may also be performed as part of medical screening examinations. In some cases, AST may be useful in monitoring the course of myocardial infarction. Where recent myocardial infarction is suspected, AST has a diagnostic sensitivity of 96%, with a diagnostic sensitivity of 86% at 12 hours after onset of chest pain. AST levels may be increased in viral hepatitis and liver disease associated with hepatic necrosis, with 20 to 50 fold elevations frequently encountered.
The evaluation of AST activity in relation to ALT (De Ritis ratio; AST/ALT) is a useful indicator of liver damage. Ratios <1.0 are indicative of mild liver damage, and are particularly associated with diseases of an inflammatory nature. Ratios >1.0 are indicative of severe liver disease, usually involving necrosis. Increased AST levels may be detected in cirrhosis, extrahepatic cholestasis, progressive muscular dystrophy, dermatomyositis, acute pancreatitis, haemolytic disease, gangrene, crushed muscle injuries and pulmonary emboli.
In patients undergoing renal dialysis or those with vitamin B6 deficiency, serum AST may be decreased. The apparent reduction in AST may be related to decreased pyridoxal phosphate, the prosthetic group for AST, resulting in an increase in the ratio of apoenzyme to holoenzyme. Slight or moderate increases in AST levels may also be observed after ingestion of alcohol, or administration of drugs including penicillin, salicylates or opiates.
Method based on the recommendations of the “International Federation for Clinical Chemistry” (IFCC).
| Male (Adult) | < 50 U/L | 0.85 μkat/L |
| Female (Adult) | < 35 U/L | 0.60 μkat/L |
| Newborn | 25 − 75 U/L | 0.42 − 1.25 μkat/L |
| Infant | 15 − 60 U/L | 0.25 − 1 μkat/L |