Metabolic . Patient guide
Homocysteine Blood Test
What is Homocysteine
Homocysteine is an amino acid generated as a methylation by-product. It is cleared from the bloodstream by enzymes that depend on B12, folate, and vitamin B6, so a raised level usually reflects a functional B-vitamin shortage. It is associated with cardiovascular risk in observational studies, though large trials of lowering homocysteine with B-vitamins have not reduced cardiovascular events.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in µmol/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Optimal (functional medicine view) | under 9 | µmol/L |
| Within typical UK lab range | 9 to 15 | |
| Mildly raised (hyperhomocysteinaemia) | 15 to 30 | |
| Moderately raised | 30 to 100 | |
| Severely raised | over 100 |
What it is
When the body uses the amino acid methionine to donate methyl groups for DNA synthesis, neurotransmitter production, and detoxification, the methyl group is removed and methionine becomes homocysteine. Homocysteine is then recycled back to methionine (a B12 and folate-dependent step) or converted to cysteine (a B6-dependent step). When any of those vitamins are functionally low, homocysteine accumulates.
Why a clinician would order it
Homocysteine is checked in cardiovascular risk assessment, in unexplained cognitive decline or low mood, in stubborn fatigue or hair shedding where B-vitamin status is suspected, in recurrent miscarriage work-up, and as a sensitive functional marker of B12 / folate / B6 sufficiency that often flags an issue before any single B-vitamin level falls below the lab range.
If your level is outside the range
Symptoms of low Homocysteine
- No symptoms attributable to low homocysteine
What low can indicate. Optimal methylation status and adequate B-vitamin cofactors.
Symptoms of high Homocysteine
- Symptoms relate to the underlying vitamin deficiency or the cardiovascular consequence: fatigue, cognitive symptoms, paraesthesia, low mood, exercise intolerance
What high can indicate. Functional deficiency of B12, folate, or vitamin B6. Less commonly: hypothyroidism, renal impairment, MTHFR polymorphism affecting folate metabolism, certain medications (methotrexate, anticonvulsants), heavy alcohol use, or the inherited condition homocystinuria when severely raised.
Testing tips
Fasting strongly preferred (overnight fast, water only). Recent meals raise homocysteine transiently. Hold B-vitamin supplements for 24 hours before testing for a true baseline. Always interpret alongside B12, folate, and ideally MMA for the full methylation picture.
Where you can get this tested
Homocysteine is not part of a standard WMG Health panel, but it can be added to one. Build a custom panel and our clinicians will confirm the markers and price in writing before you book.
Looking to book a test?
Comprehensive private health screening
Full blood screening at 134 Harley Street, London, reviewed by GMC-registered doctors with a written interpretation.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Homocysteine
What is a normal Homocysteine range?
Optimal (functional medicine view): under 9 (µmol/L). Within typical UK lab range: 9 to 15. Mildly raised (hyperhomocysteinaemia): 15 to 30. Moderately raised: 30 to 100. Severely raised: over 100. Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Homocysteine result mean?
Optimal methylation status and adequate B-vitamin cofactors.
What does a high Homocysteine result mean?
Functional deficiency of B12, folate, or vitamin B6. Less commonly: hypothyroidism, renal impairment, MTHFR polymorphism affecting folate metabolism, certain medications (methotrexate, anticonvulsants), heavy alcohol use, or the inherited condition homocystinuria when severely raised.
Do I need to fast or prepare for the Homocysteine blood test?
Fasting strongly preferred (overnight fast, water only). Recent meals raise homocysteine transiently. Hold B-vitamin supplements for 24 hours before testing for a true baseline. Always interpret alongside B12, folate, and ideally MMA for the full methylation picture.
Can I order a Homocysteine blood test privately in London?
Yes. WMG Health offers Homocysteine as part of a custom panel at our 134 Harley Street clinic. Results are released as each marker is reviewed, and the completion date is set by the slowest marker in your panel. We confirm the expected timeframe at booking. Book a standard panel online, or ask for a custom panel via /contact/ or 020 3239 3378.