Interpretation
AST should be interpreted with the results of the other liver function tests.
ALT and AST are hepatocellular enzymes. An elevation of ALT and/or AST indicates damage to the hepatocytes with release of the enzyme into the circulation.
The AST/ALT ratio (De Ritis ratio) may suggest the underlying cause of the liver disease:
– AST/ALT >1 is associated with alcoholic liver disease, hepatic ischaemia and some types of viral hepatitis
– AST/ALT <1 is a common finding in non-alcoholic fatty liver disease – these patients should be screened for other features of the metabolic syndrome.
The magnitude of elevation does not always correlate with the degree of liver damage. Liver enzyme elevations in advanced cirrhosis are often relatively mild due to the paucity of functioning liver tissue. Conversely, very large elevations may occur due to hepatic ischaemia and toxin-induced necrosis (e.g. paracetamol overdose).
Non-hepatic causes of AST elevation
AST elevations are also seen with haemolysis and with disease states affecting muscle tissue (e.g. myositis, acute myocardial infarction etc.) An elevated AST but normal ALT should prompt suspicion of a non-hepatic cause. Measurement of other biomarkers (e.g. troponin, CK, haptoglobin) as indicated by the clinical context should assist in determining the source of the high AST.
Test Method
Kinetic UV test for the quantitative determination of aspartate aminotransferase performed on Beckman Coulter AU5822 analyser using Beckman Coulter reagents
