Homocysteine is a non-essential sulfur containing amino acid closely linked to the essential amino acid methionine. Homocysteine is rapidly oxidized in plasma into homocystine and cysteine- homocysteine disulfide. Total plasma homocysteine is the sum of homocysteine and its oxidized forms. The determination of total homocysteine plays an indicator role in diagnosis and therapy of folate, vitamin B12 and vitamin B6 deficiencies. In addition, several observational studies have confirmed that increased total homocysteine is an independent predictor of cardiovascular risk.