What does homocysteine measure and why is it tested?
Homocysteine is an amino acid intermediate that accumulates when B-vitamin–dependent methylation falters. Elevated homocysteine is associated with cardiovascular and cognitive risk and points toward B12, folate, B6, and methylation status.
Full answer
Homocysteine is an amino acid intermediate in methionine metabolism. Its clearance depends on adequate B12, folate, B6, and intact methylation (including the MTHFR pathway). When these inputs falter, homocysteine accumulates. Elevated homocysteine has been associated with atherosclerotic cardiovascular disease, venous thromboembolism, and cognitive decline; while supplementation to lower homocysteine has not consistently reduced cardiovascular events in randomized trials, elevated homocysteine remains a useful pointer toward upstream B-vitamin status and methylation efficiency. Provider review reads homocysteine alongside B12, folate, and clinical context before recommending repletion — and chooses the form (methylcobalamin, methylfolate vs cyanocobalamin, folic acid) based on the individual picture.
Educational. Not a substitute for individualized provider review.
- Homocysteine — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29