Homocysteine
Also called Total homocysteine, plasma homocysteine, Hcy
Homocysteine is an amino acid, one of the building blocks the body uses to make proteins. It is normally kept low because vitamin B12, vitamin B6 and folate (vitamin B9) quickly convert it into other substances the body needs, so a high level can be a sign that this process is not working or that one of those vitamins is in short supply.
A homocysteine test is most often used as an indirect check on those B vitamins. High homocysteine is associated with damage to arteries and a higher risk of blood clots, heart attack and stroke, but the relationship is uncertain enough that routine screening for heart risk is not recommended for everyone, and in most studies lowering homocysteine has not reduced heart attacks or strokes. What a high result signals, and what it does not, is covered in High Homocysteine: What It Signals and What It Does Not.
Why it matters after 45
Homocysteine tends to rise with age. Levels run higher in men than in women, but women's levels increase after menopause. Older adults also absorb vitamin B12 from food less well, which is one route to a high result, and higher levels are also seen with chronic kidney disease, an underactive thyroid and osteoporosis. That combination is why the marker appears on midlife panels, usually alongside B12 and folate.
Where it comes up
References
- MedlinePlus. Homocysteine Test. U.S. National Library of Medicine. https://medlineplus.gov/lab-tests/homocysteine-test/
- Cleveland Clinic. Homocysteine. https://my.clevelandclinic.org/health/diagnostics/21527-homocysteine
Definitions here are educational and are not medical advice. They explain what a term means; the pages linked above cover what it means for you, and a clinician reviews your own results. Editorial & medical review policy · All glossary terms