Plasma homocysteine (also known as homocysteine, Hcy) is an intermediate product in the process of methionine metabolism. Homocysteine was discovered by DeVgneaud in 1932 and its structureal formula is HSCH2 (NH2) CO2H. There are for two forms of oxidized and reduced HCY in plasma. The oxidized form contains disulfide groups include homocysteine and systine. And the reduced form contains sulfur groups include homocysteine and systeine. There is a small amount of homocysteine in the normal body, and the reduced form accounts for only 2%.