What is the Homocysteine test? Homocysteine is an amino acid that's normally present in small amounts in your blood. High levels of homocysteine can be a risk factor for several health problems.   What the Homocysteine test is used for: The Homocysteine test is primarily used to: Assess the risk of cardiovascular disease (CVD): High homocysteine levels have been linked to an increased risk of heart attacks, strokes, and blood clots.   Diagnose vitamin deficiencies: Deficiencies in vitamin B12, folate (vitamin B9), and vitamin B6 can cause elevated homocysteine levels.   Diagnose homocystinuria: A rare inherited disorder that causes very high levels of homocysteine.