Homocysteine Unit Converter
Homocysteine Unit Converter
Convert homocysteine between mg/L, µg/mL and µmol/L, and see why a raised result points more often to B12 status than to cardiovascular risk.
Homocysteine converter
Mass ⇄ molarHomocysteine 2.2 mg/L
Formula and conversion factor
mg/L = µmol/L ÷ 7.398
- 7.398
- derived from the molecular weight of homocysteine, 135.18 Da
- µg/mL
- numerically identical to mg/L
- sample handling
- separate within one hour of venepuncture — red cells continue releasing homocysteine into plasma after collection, raising the result if delayed
Worked example
Homocysteine 2.2 mg/L
2.2 × 7.398 = 16.3 µmol/L
= 2.2 µg/mL
Reference range and thresholds
| mg/L | µmol/L | |
|---|---|---|
| Adult reference interval | 0.68 – 2.03 | 5 – 15 |
| Typical mild elevation (B12/folate deficiency) | 2.03 – 4.06 | 15 – 30 |
| Homocystinuria, untreated | > 13.5 | > 100 |
What homocysteine measures
Most laboratories now report homocysteine directly in µmol/L, though some send-away assays still issue results in mg/L, and confusing the two produces a large numerical error given a conversion factor of roughly 7.4. Homocysteine is an intermediate in methionine metabolism, cleared either by remethylation back to methionine — which needs vitamin B12 and folate as cofactors — or by transsulfuration to cystathionine, which needs vitamin B6. A block anywhere in that pathway raises the level.
Raised homocysteine is most often a marker of B12, folate or B6 deficiency, and it is a more sensitive marker of tissue B12 deficiency than serum B12 itself, since serum B12 measures a circulating pool that is not entirely metabolically available. It also rises with renal impairment, hypothyroidism, methotrexate, and in people carrying MTHFR gene variants, none of which reflect vitamin status.
Be candid about the cardiovascular question. Homocysteine is consistently associated with vascular disease in observational studies, but the randomised trials of B-vitamin lowering — NORVIT, HOPE-2 and SEARCH among them — did not reduce cardiovascular events despite reliably lowering the level. It should be read as a marker rather than a modifiable treatment target outside specific deficiency states.
Where homocysteine genuinely earns its place is in diagnosing B12 deficiency alongside methylmalonic acid, and in homocystinuria, where levels are extreme and treatment changes outcome substantially. The sample itself needs care: homocysteine leaks continuously from red blood cells after venepuncture, and plasma must be separated within an hour or the result reads falsely high.
Frequently asked questions
How do I convert homocysteine from mg/L to µmol/L?
Multiply by 7.398 — derived from its molecular weight of 135.18 Da. A homocysteine of 2.2 mg/L is 16.3 µmol/L.
What is the most common cause of raised homocysteine?
Deficiency of vitamin B12, folate or B6. It is a more sensitive marker of tissue B12 deficiency than serum B12 itself.
Does lowering homocysteine reduce cardiovascular risk?
There is no convincing evidence that it does. Homocysteine is associated with vascular disease, but the major B-vitamin lowering trials — NORVIT, HOPE-2, SEARCH — did not reduce cardiovascular events despite lowering the level.
Why does the sample need to be separated so quickly?
Homocysteine continues to leak from red blood cells after the sample is drawn. A delay of more than an hour before separation raises the measured value independently of the patient’s true level.
Related calculators
References
- Bønaa KH, Njølstad I, Ueland PM, et al. Homocysteine lowering and cardiovascular events after acute myocardial infarction. N Engl J Med. 2006;354(15):1578–1588.
- Refsum H, Smith AD, Ueland PM, et al. Facts and recommendations about total homocysteine determinations: an expert opinion. Clin Chem. 2004;50(1):3–32.