Homocysteine can be used by clinicians as a aid in the diagnosis of inherited disorders of methionine metabolism including cystathionine synthase deficiency (homocystinuria), methylenetetrahydrofolate reductase deficiency and its thermolabile variants, and methionine synthase deficiency and can be used for evaluating patients for suspected deficiency of vitamin B12 or folate.
Homocysteine is an intermediary in the sulphur-amino acid metabolism pathways, linking the methionine cycle to the folate cycle. Several primary and secondary disorders of methionine metabolism may be diagnosed based on measurement of homocysteine in plasma and urine.
Inborn errors that lead to homocysteinemia/-uria involving defects in the primary enzyme include cystathionine synthase deficiency (homocystinuria), methylenetetrahydrofolate reductase deficiency and thermolabile variants, and methionine synthase (MS) deficiency. Genetic defects in vitamin cofactors (vitamin B6, B12, and folate) and nutritional deficiency of B12 and folate also lead to abnormal homocysteine accumulation.
Homocysteine concentration is an indicator of acquired folate or cobalamin deficiency, and is a contributing factor in the pathogenesis of neural tube defects.
5 – 15 µmol/L
Plasma – EDTA. Plasma needs to be separated from cells within 1 hour of venepuncture. Once separated refrigerate sample until can be sent via 1st class post.
Plasma homocysteine may be falsely raised if there a delay in separating cells >30 mins, renal impairment, or B12/folate deficiency.
University Hospital of Wales