TISSUE INJURY & ISCHEMIA

• Aspartate aminotransferases (AST) and lactate dehydrogenase (LDH) are sometimes used as markers for tissue damage, though nonspecific (both enzymes are found diffusely throughout the body in various tissue types).
   AST: transfers amino groups from aspartate to α-ketoglutarate (part of citric acid cycle), found in cytosol and mitochondria
   LDH: converts pyruvate to lactate, found in cytosol
   Clinically, AST is often used in the diagnosis of liver diseases as part of the liver function tests (LFTs) and LDH is used to diagnose hemolytic anemias and hematologic malignancies
• On the other hand, lactate, which is converted from pyruvate by LDH during anaerobic glycolysis, is often used as a marker for tissue hypoperfusion/ ischemia.
   However, lactate is also elevated in impaired cellular metabolism in the absence of tissue hypoperfusion/ ischemia.