Homocysteine [Hcy; HSCH2CH2CH(NH3)+COO-], a homolog of cysteine, is a non-protein α-amino acid. It is produced from methionine by the removal of its terminal Cε methyl group, and is an intermediate in the biosynthesis of L-cysteine from L-methionine via L-cystationine. Homocysteine can be recycled into methionine or converted into cysteine with the help of B-vitamins. It has been observed that a high level of homocysteine makes a person more prone to endothelial injury. High level of homocysteine can lead to vascular inflammation, which in turn may lead to atherogenesis, and ultimately resulting in ischemic injury.
Amino acid analysis allows for the quantitative analysis of homocysteine in biological samples such as serum and blood plasma.