Homocysteine
An amino acid that rises when B vitamins are insufficient, associated with cardiovascular and cognitive risk.
| Typical reference range | below 15 umol/L |
| Commonly cited optimal range | below 9 umol/L |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Homocysteine is made from methionine during methylation. It is recycled back to methionine using folate and B12, or converted to cysteine using vitamin B6. Deficiencies in these vitamins cause it to accumulate.
Why it matters
Elevated homocysteine is associated with heart disease, stroke, blood clots, cognitive decline and pregnancy complications, and is a functional marker of B12 and folate status. Lowering it with B vitamins has shown benefit for stroke in some trials but not clearly for heart attacks.
What a high result can mean
Causes include low folate, B12 or B6, kidney disease, hypothyroidism, smoking, heavy coffee or alcohol intake, older age, MTHFR gene variants (with low folate), and medications such as methotrexate, metformin, proton pump inhibitors and some anticonvulsants.
What a low result can mean
Low levels are generally not a concern; very low values may occur with high B-vitamin supplementation.
What affects the result
Fasting is preferred, as protein-rich meals can raise it. The sample must be processed promptly or levels rise falsely. Folate, B12 and B6 intake lower it. Interpret with B12, folate, MMA and kidney function.
Units and conversion
Usually reported in umol/L.
- From nmol/mL: multiply by 1 to get umol/L
- From mg/L: multiply by 7.397 to get umol/L
Also called on lab reports
Homocysteine, Plasma, Homocyst(e)ine, Total Homocysteine, Hcy, Homocysteine, Total, Homocysteine, Serum
Related tests: Heart
This page is educational and does not replace advice from a healthcare professional.