Homocysteine is an amino acid normally found in small amounts in the blood. Although the exact relationship is unclear, high levels of homocysteine in the blood are thought to promote plaque buildup in blood vessels that may, over time, lead to serious cardiovascular disease such as stroke, heart attack, pulmonary embolism, and deep vein thrombosis.

People who have a strong personal or family history of heart disease but who do not have other risk factors that can be controlled, such as smoking or high blood pressure, may benefit from having a blood test to determine their homocysteine levels. This information can help a doctor determine a person's overall risk for heart disease.