Aspartate aminotransferase transaminase

ASPARATE AMINOTRANSFERASE TRANSAMINASE (AST)
  • Two AST isoenzymes are found, one cytosolic and one mitochondrial. The half life is reported to be about 12 hours in dogs. This enzyme is released into the blood with increased cell membrane permeability and cellular necrosis (when the mitochondrial isoenzyme is released).
  • Like ALT, the magnitude of increase said to be proportional to the number of hepatocytes injured but does not indicate the functional status of the organ. It is reported to be a good indicator of degree of necrosis as well as a good screening test with a sensitivity of 88%.
  • Since AST is found in many organs, including muscle, heart and liver it is not a specific indicator of hepatic damage and if elevations occur in the absence of elevations of ALT, measurement of serum Creatine kinase, a muscle specific enzyme, may be required to rule out muscle damage.
  • Since AST does not appear to have an advantage over ALT as a marker of hepatocyte damage in terms of liver specificity, its value as an additional test should be questioned. It is not routinely used to assess hepatic injury in dogs as it does not appear to have an advantage over ALT as a marker of hepatocyte damage. However, AST was increased in 2/3 of 14 dogs with hepatic abscesses. In the late stages of hepatic lipidosis when the lipid accumulation becomes excessive, AST is reported to elevate.
  • Increased AST is reported to be a sensitive indicator of metastatic (secondary) liver disease in dogs. The author's institution does not, generally, make use of this enzyme in dogs, preferring to rely on ALT and ALP.
  • Until time-and-while a novel serum, liver-specific enzyme is proposed, the use of ALT and ALP (with the possible occasional use of GDH), probably supplies the average veterinary clinician with sufficient information about hepatocyte integrity, cholestasis and steroid induction provided that the limited sensitivity and poor predictive value are borne in mind.
Last modified: Wednesday, 22 February 2012, 5:51 AM