Homocystine (also referred to as Homocysteine), when mildly elevated, has been discovered to be a risk factor for vascular disease and thromboembolism (myocardial infarction, stroke, peripheral vascular disease, deep vein thrombosis, and retinal thrombosis). The mechanism for this is unclear but increased levels of homocysteine have been associated with toxicity to the walls of the arteries and enhanced blood clotting. Moderate hyperhomocystinemia is found in 20-40% of patients with vascular disorders.

It is not yet clear whether all persons should undergo testing for this risk factor. It is certainly recommended in persons with known vascular problems and persons with a family history. If the test is carried out and the Homocysteine is found to be elevated, patients can be treated using folic acid and Vitamin B12.  This is because Homocysteine is a component of the B12/Folate metabolic pathway.  If this approach is not successful, Pyridoxine (Vitamin B6) can be added to the regime.