Homocysteine, plasma or serum

Homocysteine (HCY) is a thiol-containing amino acid produced by the intracellular demethylation of methionine. Homocysteine accumulates and is excreted into the blood when these reactions are impaired. Impaired homocysteine metabolism results in hyperhomocysteinemia (increased levels of homocysteine in plasma or serum) or homocystinuria (high plasma levels cause homocysteine to be excreted in urine). Hyperhomocysteinemia is caused by nutritional and genetic deficiencies. The majority of elevated homocysteine cases (two-thirds) in the general population are due to deficiency of folic acid, vitamin B6 and vitamin B12. Severely elevated concentrations of total homocysteine are found in subjects with homocystinuria, a rare genetic disorder of the enzymes involved in the metabolism of homocysteine. Studies have investigated the relationship between elevated homocysteine concentrations and cardiovascular disease (CVD), indicating homocysteine as an important marker for risk assessment