Homocysteine
VitaminsHomocysteine is an amino acid your body makes when it processes protein from food.
Also known as: Hcy, tHcy, total homocysteine, plasma homocysteine
It normally doesn't build up, because your body recycles or breaks it down with the help of vitamin B12, folate and vitamin B6. When one of these runs short, homocysteine rises in the blood, often before the vitamin level itself looks clearly low. That makes it a useful check alongside B12 and folate: it shows whether your body actually has enough of them to work with. A raised value isn't only about vitamins, though. Reduced kidney function, an underactive thyroid, some medicines (such as metformin, methotrexate or certain epilepsy drugs), smoking, a lot of coffee, older age and inherited differences such as MTHFR variants can all raise it. Raised homocysteine is also linked to a higher risk of heart attack and stroke, but lowering it with B-vitamins has not been shown to prevent heart attacks. At Ahead it is measured together with B12 and folate, mainly to check whether your body has enough of these vitamins.
Reference range
| Level | Range |
|---|---|
| High | above 15 μmol/l |
| Normal | 10 to 15 μmol/l |
| Low | below 10 μmol/l |
Source: Ahead Health benchmark
* Reference ranges may vary between labs and assays. Always interpret results with your healthcare provider.
Why this matters
High homocysteine damages blood vessel walls, promotes inflammation, and increases blood clotting risk, significantly elevating the risk of heart disease, stroke, and dementia, even without symptoms. It may also contribute to osteoporosis and pregnancy complications. Low levels are rare but usually benign. Homocysteine is influenced by B vitamin intake (especially folate, B12, and B6), genetics (MTHFR gene variants), kidney function, and lifestyle factors like smoking and coffee consumption.
Monitoring helps identify cardiovascular risk that cholesterol tests might miss, and elevated levels can often be lowered through B vitamin supplementation and dietary improvements, reducing long-term disease risk.
How this connects to other biomarkers
- Homocysteine elevation with low B vitamins indicates supplementation could reduce cardiovascular and dementia risk.
- High homocysteine with kidney dysfunction reveals another cardiovascular risk factor in kidney disease requiring management.
How often should I test Homocysteine?
There is no routine schedule for testing homocysteine in healthy adults. It is most useful together with B12 and folate if you eat little or no animal food, are over 60, take metformin or acid-reducing medication long-term, or have had a borderline B12 result. If your value is raised, retest about 3 months after starting B-vitamins or changing your diet, to see whether it has come down.
At baseline / for screening: Once, together with B12 and folate, if you eat little or no animal food, are over 60, take metformin or acid-reducing medication long-term, or have had a borderline B12 result.
When monitoring an intervention or change: About 3 months after starting B-vitamins or changing your diet, to confirm the level is coming down.
Note: Homocysteine is best measured fasting, because a protein-rich meal can raise it slightly for several hours. Kidney function, some medicines and smoking also raise it, so a single raised value is best read together with your B12 and folate results.
Sources
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