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Homocysteine A clue to low B12 or folate

Also called Homocyst(e)ine, Total homocysteine and tHcy Not on a standard checkup Fasting preferred

The short answer

Homocysteine is an amino acid that builds up in your blood when you’re short of B12 or folate. Under 15 µmol/L is normal.4,7 Higher homocysteine is linked to heart disease, but lowering it with folate or other B vitamins hasn’t reduced heart attacks or deaths in randomized trials.1,2 So it’s worth testing as a clue to low B12 or folate, not as a heart test.

A good result
Under 15 µmol/L. Lab ranges run a little higher as you get older.4
If yours is high
Check B12 and folate. Low B12 is the most common nutritional cause, and worth treating for your nerves and blood.4,5
Should you test?
Not routinely for heart risk.8 It’s useful if you might be low in B12, for example on metformin or a vegan diet.5

Check your result

Type the number from your report. It stays on this page.

15 30 100
  • Normal Under 15.0
  • Mildly high 15.0 to 29.9
  • Intermediate 30.0 to 99.9
  • Very high 100.0 or more

Enter your result to see what it means and what to do next.

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Bands as experts commonly group them.7 Your lab’s cutoff may be a little lower or higher, depending on your age.4 The bar isn’t to scale.

What is a normal homocysteine level?

Most labs flag a result over about 15 µmol/L, and their ranges rise with age.4 Above that, high levels are usually grouped into three bands:7

Normal Under 15 µmol/L

Normal

Your level is normal. Homocysteine tends to rise quickly when B12 runs low, so this is a reassuring sign.5

How worried to be

Nothing to worry about.

What to do next
  1. 1 Nothing to do. Taking B vitamins to push it lower hasn’t been shown to prevent heart attacks.2
Mildly high 15 to 29.9 µmol/L

Mildly high: check B12 and folate

This is the most common kind of high homocysteine.7 Low B12 or folate, reduced kidney function, some medicines and an inherited MTHFR variant are the usual causes.4,5,6 If you’re over 60, your lab may call the lower end of this band normal, because ranges rise with age.4

How worried to be

Not urgent. Worth finding the cause over the next few weeks.

What to do next
  1. 1 Test B12 and folate. Low B12 is the most common nutritional cause.4
  2. 2 Check your kidney function, which a metabolic panel includes.4
  3. 3 If you take metformin or an acid-reducer regularly, ask about checking your B12.5
Intermediate 30 to 99.9 µmol/L

Clearly high: find the cause

Levels this high usually have a clear cause. The most common are a marked shortage of B12 or folate and kidney failure. Less often, it’s an inherited condition.4

How worried to be

See a clinician in the next few weeks. It isn’t an emergency.

What to do next
  1. 1 Test B12, folate and kidney function.4
  2. 2 If your B12 is borderline, ask about a methylmalonic acid (MMA) test, the most sensitive check for low B12.5
  3. 3 Low B12 is usually treated with injections or high-dose tablets.5
Very high 100 µmol/L or more

Very high: see a clinician soon

Levels this high are rare. They point to a severe B12 shortage or an inherited condition such as homocystinuria, which can affect the eyes, bones and blood clotting.4

How worried to be

Book an appointment within the next week or two.

What to do next
  1. 1 Take this result to a clinician. B12, folate and kidney tests usually come first.4
  2. 2 If those don’t explain it, ask about seeing a metabolic specialist to test for homocystinuria.4
Homocysteine test, $35.00
Results in 2 to 3 days, explained in the app
Order

What is homocysteine?

Think of homocysteine as a half-finished part on an assembly line. B12, folate and B6 are the workers who finish it. When they’re short-handed, unfinished parts pile up in your blood.

Your body makes homocysteine when it breaks down methionine, an amino acid from the protein you eat. Enzymes that rely on B12, folate and B6 then recycle it or break it down.4,6 Your kidneys help clear it from your blood, so levels rise when they slow down.7

What causes high homocysteine?

  • Low B12, folate or B6. Low B12 is the most common nutritional cause.4,6
  • Kidney disease, because your kidneys clear homocysteine.4,7
  • An underactive thyroid.7
  • Your genes. Two copies of a common MTHFR variant, called C677T, are found in 10% to 15% of white North Americans and over 25% of Hispanic people. It usually causes only a mild rise, mostly when folate is low.6
  • Medicines. Methotrexate and nitrous oxide raise it directly,4 and metformin and acid-reducers can lower your B12.5
  • Smoking and coffee.7
  • Rare inherited conditions, such as homocystinuria, which cause very high levels.4

Age matters too: levels rise slowly as you get older.7

Does lowering homocysteine prevent heart attacks?

Not in trials so far. People with higher homocysteine do have more heart disease and stroke. In pooled studies, a level about 3 µmol/L lower went with an 11% lower risk of heart disease and a 19% lower risk of stroke. The authors called it a modest link at most.1

But B vitamins lower homocysteine without cutting heart attacks. A Cochrane review of 15 trials and 71,422 people, including HOPE-2, NORVIT and VITATOPS, found no difference in heart attacks or deaths.2 Strokes were slightly less common: 4.3% with B vitamins against 5.1% without.2

The clearest stroke benefit came from CSPPT, a trial of 20,702 adults with high blood pressure in China. Adding folic acid to a blood pressure pill cut first strokes from 3.4% to 2.7% over about 4.5 years, and the authors linked the benefit to low folate at the start.3 Even so, US stroke guidelines rate B vitamins for preventing a first stroke as not well established.10 The US adds folic acid to grain products, which has raised folate and lowered homocysteine across the population.6

So the reason to test homocysteine is to find a B12 or folate shortage, which is worth treating for its own sake. It isn’t a heart-risk number to push down.

How to lower homocysteine

  • Treating low B12

    Injections or high-dose tablets.5 Low B12 is the most common nutritional cause of high homocysteine.4

    How much it helps
    A lot
    How sure we are
    Very sure
  • Folic acid and other B vitamins

    Lower homocysteine, but haven’t prevented heart attacks in trials.2

    How much it helps
    Some
    How sure we are
    Very sure
  • Not smoking

    Smoking is linked to higher levels.7

    How much it helps
    A little
    How sure we are
    Early evidence

Because a lower number hasn’t meant fewer heart attacks, the reason to treat is the vitamin shortage itself.2,5

Should you get an MTHFR gene test?

Usually not. The American College of Medical Genetics and Genomics says MTHFR testing has little clinical use.6 If your homocysteine is high, B12, folate and kidney tests tell you more, because those causes can be treated.4

If you already know you have two copies of the variant, there’s no evidence it raises your risk of dying, from heart disease or anything else.6

Who should get a homocysteine test?

It isn’t a routine heart test. European guidelines advise against routinely measuring extra blood markers like this for heart risk,8 and the 2026 US cholesterol guideline leaves it off its list of risk enhancers.9

It can help if:

  • You might be low in B12: you’re older, eat a vegan or vegetarian diet, have had stomach or bowel surgery or have pernicious anemia.5
  • You’ve taken metformin or an acid-reducer for a long time.5
  • Your B12 result is borderline. MMA is the more specific follow-up; homocysteine rises too, but has more other causes.5
  • You’ve had a blood clot at a young age without a clear cause. Rarely, this points to homocystinuria.4

How to get a homocysteine test, and what it costs

A homocysteine test costs $35.00 through Picardo.

Order the test

Homocysteine test

$35.00
Labcorp 706994 · fasting preferred
Order homocysteine
  • Results in 2 to 3 days, in the app
  • Physician follow-up if you want one
  • Free Labcorp draw, or $75 at home
  • No other fees. HSA and FSA eligible.
Already have a result? Ask Picardo about it

Questions people ask

Is high homocysteine linked to memory loss?

Possibly. Some studies link high homocysteine and low B12 to poorer memory and thinking, but others don’t. In trials, B vitamins didn’t improve memory in older adults, with or without dementia.5

Does homocysteine go up with age?

Yes. Levels rise with age, so lab ranges are higher for older adults.4,7 Older adults are also more likely to be low in B12, often because they absorb it less well.5

Can a vegan diet raise homocysteine?

It can, through low B12. Natural B12 comes only from animal foods, so vegans need fortified foods, such as some cereals and nutritional yeasts, or a supplement.5

Does high homocysteine cause blood clots?

Very high levels, as in homocystinuria, raise the risk of clots.4 Mildly high levels have been linked to a smaller rise in clot risk.6

Often checked alongside

Vitamin B12
Needed for nerves and red blood cells
Folate
A B vitamin for cell growth
hs-CRP
Low-grade inflammation linked to heart risk
Creatinine
Muscle waste the kidneys filter out

Test details

Labcorp test
Homocyst(e)ine, 706994
LOINC
13965-9
Sample
Blood
Fasting
Preferred
Typical lab range
0 to 14.5 µmol/L at ages 18 to 60; up to 17.2 at 61 to 70, 19.2 at 71 to 80 and 21.3 over 80
Units
µmol/L. For mg/L, divide by 7.4.

Sources

  1. 1 Homocysteine Studies Collaboration. Homocysteine and risk of ischemic heart disease and stroke: a meta-analysis. JAMA. 2002;288(16):2015–2022. doi.org/10.1001/jama.288.16.2015
  2. 2 Martí-Carvajal AJ, Solà I, Lathyris D, Dayer M. Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev. 2017;8(8):CD006612. doi.org/10.1002/14651858.CD006612.pub5
  3. 3 Huo Y, Li J, Qin X, et al. Efficacy of folic acid therapy in primary prevention of stroke among adults with hypertension in China: the CSPPT randomized clinical trial. JAMA. 2015;313(13):1325–1335. doi.org/10.1001/jama.2015.2274
  4. 4 Morris AAM, Kožich V, Santra S, et al. Guidelines for the diagnosis and management of cystathionine beta-synthase deficiency. J Inherit Metab Dis. 2017;40(1):49–74. doi.org/10.1007/s10545-016-9979-0
  5. 5 Office of Dietary Supplements, National Institutes of Health. Vitamin B12: fact sheet for health professionals. ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
  6. 6 Hickey SE, Curry CJ, Toriello HV. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing. Genet Med. 2013;15(2):153–156. doi.org/10.1038/gim.2012.165
  7. 7 Ganguly P, Alam SF. Role of homocysteine in the development of cardiovascular disease. Nutr J. 2015;14:6. doi.org/10.1186/1475-2891-14-6
  8. 8 Visseren FLJ, Mach F, Smulders YM, et al. 2021 ESC Guidelines on cardiovascular disease prevention in clinical practice. Eur Heart J. 2021;42(34):3227–3337. doi.org/10.1093/eurheartj/ehab484
  9. 9 Blumenthal RS, Morris PB, Gaudino M, et al. 2026 ACC/AHA/AACVPR/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of dyslipidemia: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2026;153(17):e1154–e1276. doi.org/10.1161/CIR.0000000000001423
  10. 10 Bushnell C, Kernan WN, Sharrief AZ, et al. 2024 guideline for the primary prevention of stroke: a guideline from the American Heart Association/American Stroke Association. Stroke. 2024;55(12):e344–e424. doi.org/10.1161/STR.0000000000000475

Updated 4 Nov 2026.

This is general health information, not medical advice: talk to your clinician about your results and before changing any treatment.