What is Homocysteine?
Homocysteine is a sulphur-containing amino acid formed during the metabolism of methionine. It is cleared by two vitamin-dependent routes: remethylation to methionine, requiring folate and vitamin B12, and transsulphuration to cysteine, requiring vitamin B6. Because these pathways depend on B-vitamin cofactors and adequate renal clearance, plasma homocysteine rises when any of these is deficient or impaired. It circulates largely protein-bound, and the analyte is labile in whole blood, continuing to be released from red cells if the specimen is not processed promptly.