Myeloperoxidase (MPO) is a peroxidase enzyme and a marker of inflammation and neutrophil activation during strenuous exercise. In addition, it has been implicated in the oxidation of lipids contained in low-density lipoproteins, infiltration of macrophages and neutrophils, formation of unstable coronary plaques, and plaque rupture. MPO is elevated in patients with coronary artery disease and can be a prognostic marker for identifying patients with unstable plaques before complete microvascular obstruction. MPO serves as a risk marker for atherosclerosis and coronary artery disease, predicting the early risk of myocardial infarction. Quantitative assays for MPO are based on the antibody sandwich principle using ELISA or CLIA.