Homocysteine is a sulfur-containing amino acid produced during the metabolism of methionine, an essential amino acid obtained from dietary protein. Plasma homocysteine levels reflect the balance between its production and its remethylation back to methionine (requiring folate and vitamin B12) or transsulfuration to cystathionine (requiring vitamin B6). Elevated homocysteine, termed hyperhomocysteinemia, is associated with increased cardiovascular, cerebrovascular, and thromboembolic risk, though the nature of this relationship remains an area of active investigation. Homocysteine is generated intracellularly when S-adenosylmethionine donates its methyl group during methylation reactions, ultimately yielding homocysteine as a byproduct. It is either remethylated to methionine via methionine synthase (dependent on vitamin B12 and 5-methyltetrahydrofolate) or irreversibly catabolized through the transsulfuration pathway via cystathionine beta-synthase (dependent on vitamin B6 and pyridoxal phosphate). Deficiencies in folate, vitamin B12, or vitamin B6, as well as genetic polymorphisms such as MTHFR C677T, can impair these pathways and lead to homocysteine accumulation.
Homocysteine is a sulfur-containing amino acid formed during methionine metabolism. Its clearance depends on B12, B6, and folate as enzymatic cofactors. Elevated homocysteine is an independent risk factor for cardiovascular disease and is used clinically to assess both cardiovascular risk and functional B-vitamin status.
Elevated homocysteine (>15 µmol/L) is associated with endothelial dysfunction, increased thrombotic risk, and accelerated atherosclerosis. Common causes include B12, B6, or folate deficiency, renal impairment, hypothyroidism, and MTHFR polymorphisms that reduce enzymatic conversion efficiency.
High-protein diets increase methionine intake, which can elevate homocysteine if B-vitamin cofactors are insufficient. Individuals with MTHFR C677T or A1298C variants have reduced capacity to convert homocysteine to methionine via the folate cycle. Homocysteine is an actionable marker — elevations driven by B-vitamin insufficiency typically normalize with targeted repletion.
Turnaround Time
3 days (up to 13 days)
Fasting Required
No
Order online
Choose your lab and check out. We send your lab requisition automatically — no doctor visit needed.
Get your sample collected
Visit a lab service center near you for a quick blood draw (or book at-home phlebotomy where available).
See your results
Your results land in your Insider portal, ready to review and act on — that easy.
Your price
$12.90$40
3.1× less than retail
Versus the typical direct-to-consumer retail price for this test (illustrative — consumer prices vary by provider and region).
$12.90
$28.90
$49.90
Peer-reviewed sources supporting the educational content on this page.
