Homocysteine

Also written as: Hcy, plasma homocysteine, total homocysteine

An amino acid tied to B-vitamin status, studied as a marker of cardiovascular risk.

What it measures

The level of homocysteine, an amino acid the body produces while processing protein. Clearing it from the blood depends on folate, vitamin B12, and vitamin B6, so the level partly reflects how well supplied the body is with those vitamins.

Why a doctor orders it

Sometimes ordered when a shortage of vitamin B12 or folate is suspected, because homocysteine rises early when those vitamins run low. It is occasionally checked when unusual blood clots or early cardiovascular disease run in a family.

What is generally associated with a higher result

Broadly associated with low folate, vitamin B12, or vitamin B6, with reduced kidney function, and with a common inherited variation in the MTHFR gene that slows homocysteine processing. It has been studied as a cardiovascular risk marker, although lowering it has not clearly been shown to prevent heart disease.

What is generally associated with a lower result

Low values are generally not pursued.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

Eating before the draw - a protein-rich meal can raise it
Delays in processing the blood sample, which push the measured level up
Smoking and heavy coffee intake
Some common medicines, including metformin and certain anti-seizure drugs
Kidney function

Questions to take to your appointment

Should vitamin B12 and folate levels be checked alongside this?
Was this a fasting sample, and does that matter for how it is read?
Could my kidney function or a medicine I take be influencing the level?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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