Гомоцистеин (HCY)

The Homocysteine test (plasma total homocysteine) is used to evaluate suspected homocystinuria, particularly in infants and children with a family history of the disorder or an abnormal newborn screen. When an initial newborn screen suggests disease, measurement of homocysteine in blood and urine supports diagnostic confirmation. The assay also assists in the assessment of individuals at increased risk for myocardial infarction or stroke and in those with a familial predisposition to coronary artery disease. Use alongside clinical findings and other laboratory data to guide further evaluation.

Homocysteine is a sulfur-containing amino acid generated during methionine metabolism. Intracellular concentrations are normally low, as homocysteine is rapidly metabolized through remethylation and transsulfuration pathways that require vitamins B6, B12, and folate as cofactors. Deficiency of these vitamins can raise circulating homocysteine concentrations. Elevated homocysteine has been associated with vascular injury and thrombosis; however, randomized trials of folic acid and B‑vitamin supplementation did not reduce cardiovascular event rates, so the value of homocysteine as a solitary predictor of cardiovascular risk remains uncertain. Marked elevations occur in homocystinuria, an inherited disorder most commonly due to cystathionine beta‑synthase deficiency. Impaired enzyme activity leads to accumulation of homocysteine and methionine. Affected infants may appear well initially, with features emerging over time, including ectopia lentis, a tall, slender (marfanoid) habitus with long, thin fingers, skeletal abnormalities, and osteoporosis. Thromboembolism and premature atherosclerosis can develop, resulting in early cardiovascular disease, and later complications may include developmental delay, behavioral disturbance, and epilepsy. When homocystinuria is confirmed biochemically, tissue studies for cystathionine beta‑synthase activity and, in some settings, molecular testing are used to define the underlying defect, especially in families with known disease or early-onset atherosclerosis.