For clinicians

Homocysteine

Unit
μmol/L

What is Homocysteine?

Homocysteine is an amino acid that your body normally breaks down again with the help of B vitamins. A raised value often points to a shortage of those vitamins. Staying neatly within range supports your blood vessels and your nervous system. It's a marker you can often adjust well with diet.

Clinical frame

Homocysteine is a sulphur-containing amino acid from methionine metabolism. Its breakdown requires folate, vitamin B12 and B6, so deficiencies, MTHFR variants and renal insufficiency raise the level. Observationally, an elevated value is associated with mortality, atherosclerosis, peripheral arterial disease, venous thrombosis and stroke, with a continuous, dose-dependent relationship [1].

The causal role is vascular-bed specific: genetic studies support an effect on stroke, especially ischaemic and small-vessel stroke, but not on coronary disease, heart failure or atrial fibrillation. Large trials with B vitamins lowered homocysteine by a quarter without fewer infarctions or deaths, with at most a small reduction in strokes [2] [3].

A moderate elevation is therefore above all a weak risk marker, not a treatment target in itself. Above about 30 μmol/L the meaning changes: the value then usually points to a B12 or folate deficiency, a hereditary enzyme defect or kidney failure and warrants targeted diagnostics and correction [1] [3].

What moves this value?

Too little folate, vitamin B12 or B6 is the most common cause. Heredity and your kidney function also play a part.

Green vegetables (folate), wholegrain products and enough B12 support this. Easy to retest after a few months. Discuss a persistently high value with your doctor.

What this connects

Developed and reviewed with the Synapse medical advisory board.

References

  1. Smith, A. D. & Refsum, H. Homocysteine - from disease biomarker to disease prevention. J Intern Med 290, 826–854 (2021). doi.org/10.1111/joim.13279
  2. Yuan, S., Mason, A. M., Carter, P., Burgess, S. & Larsson, S. C. Homocysteine, B vitamins, and cardiovascular disease: a Mendelian randomization study. BMC Med 19, 97 (2021). doi.org/10.1186/s12916-021-01977-8
  3. Martí-Carvajal, A. J., Solà, I., Lathyris, D. & Dayer, M. Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev 8, CD006612 (2017). doi.org/10.1002/14651858.CD006612.pub5

The colour zones are personal: they depend on age, sex, risk and history, and appear in the patient's own report.

Insights to discuss with the patient, not a diagnostic instrument.