Homocysteine
Homocysteine is an amino-acid intermediate whose level rises when B12, folate or B6 are low. Severe elevation is also a marker of cardiovascular and dementia risk.
What it measures
Homocysteine is produced when the body breaks down methionine (from dietary protein) and is normally recycled with the help of vitamin B12, folate and vitamin B6. Deficiency of any of those vitamins blocks the recycle and homocysteine rises. The test is most useful as an early functional marker of B-vitamin deficiency — often abnormal before overt B12/folate readings move — and as a cardiovascular-risk signal when severely elevated.
What a high value can mean
- B12 or folate deficiency — by far the commonest cause; corrects with supplementation.
- Vitamin B6 deficiency — less common.
- Chronic kidney disease — impaired clearance.
- Hypothyroidism — slows the metabolism of homocysteine.
- MTHFR genetic variants — modest elevation; clinical relevance debated.
- Severe hyperhomocysteinaemia (>100 µmol/L) — classical homocystinuria; rare inherited condition with early thrombosis and skeletal abnormalities.
What a low value can mean
- Generally favourable; no intervention.
When to discuss with a doctor
Mild-moderate elevation usually responds to B12 + folate replacement. Severe elevation (>50–100 µmol/L) warrants specialist review for thrombosis risk and inherited homocystinuria. Mediora.AI flags the threshold; do not start B-vitamin therapy without confirming B12 and folate first — folate alone can mask undiagnosed B12 deficiency.