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Homocysteine
A methionine-cycle amino acid. Elevated levels are linked to vascular risk and to folate and B12 deficiency.
Other names: Homocysteine, total homocysteineSection: Blood chemistry
Updated: August 31, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortHomocysteine accumulates when folate, B12, or B6 are lacking, or when the recycling enzymes are genetically slow. A usual range is up to about 15 µmol/L (0.20 mg/dL); 15–30 µmol/L (0.20–0.41 mg/dL) is a moderate elevation. The most common cause is folate or B12 deficiency.
Reference ranges
Group
Reference range
Usual range — typical range (international reference, not a national standard)
up to about 11–15 µmol/L (up to 0.15–0.20 mg/dL)
Moderate elevation — typical range (international reference, not a national standard)
15–30 µmol/L (0.20–0.41 mg/dL)
Marked elevation — typical range (international reference, not a national standard)
30–100 µmol/L (0.41–1.35 mg/dL)
Severe elevation — typical range (international reference, not a national standard)
> 100 µmol/L (> 1.35 mg/dL)
Gradation from Lab Tests Online (international reference, not a national standard). The cutoff varies between laboratories — the report's reference applies.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Homocysteine is an intermediate of methionine metabolism, recycled with the help of folate and vitamins B12 and B6. When recycling fails, it builds up and damages vessel walls.
Testing is used after early thrombosis, in pregnancy planning alongside folate, and when B12 deficiency is suspected; kidney disease raises the level too.
When it is high
Folate and B12 deficiencyThe most common cause of moderate elevation; corrected by replenishing the deficit as the provider advises.
Kidney diseaseReduced clearance raises the level.
MTHFR variantsSlow recycling enzymes; with marked elevation the provider may order genetic testing.
HomocystinuriaA rare inherited disease with very high values (above 100 µmol/L — 1.35 mg/dL).
When it is low
Not clinically meaningfulLow homocysteine is not considered a problem.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Folate and B12 statusKidney functionMetformin and anticonvulsantsSmoking and coffee
How to prepare
Fasting 8–12 hours. Some medicines (metformin, anticonvulsants) affect the level — the provider is informed.
When a retest makes sense
An elevated result is rechecked after 1–2 months of provider-guided vitamin correction.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; a cardiologist or obstetrician-gynecologist as appropriate. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: HomocysteineTotal homocysteineHcy
Units and conversion
Measured in: µmol/L
µmol/L=mg/dL
mg/dL = µmol/L × 0.0135. Results are rounded to 2 decimal places.
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
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