High myeloperoxidase is caused by inflammation in the individual’s body or by tumors, cancer, or coronary artery system disease. In laboratory tests, myeloperoxidase represents damage to endothelial cells in the body, commonly due to inflammation of blood vessels or elevated blood lipid concentrations, which leads to thickening of the blood and agglomeration of other substances such as platelets and lipid factors in the blood in the lining of blood vessels, resulting in coronary artery system disease in the body and an increase in myeloperoxidase. If there is cardiovascular disease, especially after increased pressure and damage to cardiomyocytes, various types of inflammatory cells and cardiac enzymes rise rapidly, which also causes compensatory increase of myeloperoxidase in the body. The presence of immune reactive diseases, such as tumors and cancers, and damage to the immune system in the human body can also lead to high myeloperoxidase.