Lactate dehydrogenase (LDH or LD) is an enzyme found in nearly all living cells (animals, plants, and prokaryotes). LDH catalyzes the conversion of lactate to pyruvic acid and back, as it converts NAD+ to NADH and back. A dehydrogenase is an enzyme that transfers a hydride from one molecule to another. LDH is expressed extensively in body tissues, such as blood cells and heart muscle. Because it is released during tissue damage, it is a marker of common injuries and disease such as heart failure. LDH is a protein that normally appears throughout the body in small amounts. Many cancers can raise LDH levels, so LDH may be used as a tumor marker. Measuring LDH levels can be helpful in monitoring treatment of cancer.Lactate dehydrogenase (LDH) is cytoplasmic, and isoenzymes are tetramers of either heart (H) or muscle subunits (M). All tissues contain various amounts of the 5 LDH isoenzymes; however, muscle, liver, and red blood cells (hemolysis) are the major sources of serum LDH activity. The isoenzymes can be separated by electrophoresis. The liver isoenzyme is a less sensitive indicator of hepatotoxicity than the aminotransferases. LDH half-life is reported as less than 6 hours in dogs. Due to its lack of specificity, LDH is rarely included in non-clinical safety studies and there is little merit in LDH isoenzyme determination. Species differences exist in the predominant tissue source of CK and LDH serum activities.


1.Graham S. Smith etal, in Haschek and Rousseaux's Handbook of Toxicologic Pathology (Third Edition), 2013