Lactate dehydrogenase (LDH) can oxidize lactic acid to pyruvic acid, the enzyme is present in cells capable of glycolysis, and the enzyme is released when the cell is injured and dies.There are five isoenzymes of LDH, and LDH1-5 are present in different tissues, and tissues with high activity of this enzyme are the liver, skeletal muscle, and normal red blood cells, which have about 100-fold higher activity than serum.LDH1 is H-type (cardiac), which is related to oxygen metabolism; LDH5 is M-type (muscle), which is related to anaerobic metabolism. The LDH activity of normal erythrocytes is about 100 times higher than that of serum. LDH1 is H-type (cardiac), which is related to oxygen metabolism, and LDH5 is M-type (myocardial), which is related to anaerobic metabolism.

Lactate dehydrogenase staining solution (tetrazolium salt method) takes lactic acid as substrate, dehydrogenated under the action of enzyme, nitro blue tetrazolium ( nitro BT) is the hydrogen acceptor, after accepting hydrogen, it is reduced to methyl oxal, it is blue-purple, which is used to represent the activity of lactate dehydrogenase, but it can't differentiate what kind of LDH it is, the incubation solution for LDH contains a special intermediate hydrogen delivering body, which can make the localization more accurate, and the staining is more clear.