Type the homocysteine from your lab report, your age and your sex. You see it against Mayo Clinic Laboratories’ range for your age and sex, the cutoffs NIH ODS names and Cleveland Clinic’s bands, and what those sources say moves it. Your lab’s own range and your doctor have the last word.
Homocysteine 9 µmol/L is
Under all five high lines Mayo’s range for females, 45 years: 4.9–13.9 µmol/L
Homocysteine 9 µmol/L: inside Mayo Clinic Laboratories’ 4.9–13.9 µmol/L for females, 45 years; under the 12 to 14 band of lower cutoffs NIH ODS says have also been used; not higher than NIH ODS’s B12 line (“higher than 15 micromol/L”); inside Cleveland Clinic’s “around five to 15”; under NIH ODS’s most commonly used cutoff for elevated (16 micromol/L).
NIH ODS also names a 10 micromol/L line, for populations, not for one result: “A homocysteine cutoff of 10 micromol/L has been proposed for assessing folate status in populations” (this result is under it).
That is under every high line the sources print. The range on your own lab report is the one your doctor reads it against.
What the sources say moves it
- Mayo Clinic Laboratories: “Other factors that may influence and increase serum homocysteine include: Age; Smoking; Poor diet/cofactor deficiencies; Chronic kidney disease/renal disease; Hypothyroidism”
- NIH ODS: “Homocysteine levels, however, are not a highly specific indicator of folate status because they can be influenced by other factors, including kidney dysfunction and deficiencies of vitamin B12 and other micronutrients”
An MMA result, and a vitamin B12 on its own lines: the Vitamin B12 Level Checker. A folate result: the Folate Level Checker.
| Source | Line (µmol/L) |
|---|---|
| NIH ODS, most common cutoff | Elevated: 16 µmol/L |
| NIH ODS, lower cutoffs also used | 12 to 14 µmol/L |
| NIH ODS, B12 sheet | Higher than 15 µmol/L |
| NIH ODS, for populations | 10 µmol/L (folate status in populations) |
| Cleveland Clinic | Around 5 to 15; mild 15 to 30; moderate 30 to 100; severe more than 100 µmol/L |
| Mayo Clinic Laboratories | Its own range for each age and sex, from birth to over 85 |
This is not medical advice and it does not diagnose anything. It shows where a number sits against published lines; what your result means for you depends on your lab, your B12 and folate, your kidneys, what you take, your history and your doctor.
Cleveland Clinic: “In a healthy person, homocysteine levels are around five to 15 mcmol/L.” NIH ODS: “The most commonly used cutoff value for elevated homocysteine levels is 16 micromol/L, although slightly lower values of 12 to 14 micromol/L have also been used”. Mayo Clinic Laboratories prints its own range for each age and sex — 4.9 to 13.9 for a woman of 45, 6.6 to 14.2 for a man of 45.
How to use it
Type the homocysteine from your report in µmol/L (micromol/L, mcmol/L and nmol/mL are the same number), your age in years and your sex. You see the result against Mayo Clinic Laboratories’ range for that age and sex, the three cutoffs NIH ODS names, and Cleveland Clinic’s bands, counted as the high lines it is over, with what those sources say moves it. It does not diagnose anything: it places a number and quotes the sources.
What the test measures
MedlinePlus: “A homocysteine test measures the amount of homocysteine in a sample of your blood.” “Normally, your homocysteine levels are low.” NIH ODS on why it is read with folate: “Plasma homocysteine concentration is a commonly used functional indicator of folate status because homocysteine levels rise when the body cannot convert homocysteine to methionine due to a 5-MTHF deficiency”. And straight after: “Homocysteine levels, however, are not a highly specific indicator of folate status because they can be influenced by other factors, including kidney dysfunction and deficiencies of vitamin B12 and other micronutrients”. Mayo Clinic Laboratories: “Homocysteine concentration is an indicator of acquired folate or cobalamin deficiency and is a contributing factor in the pathogenesis of neural tube defects.”
The lines the sources print
| Source | Line (µmol/L) |
|---|---|
| NIH ODS, most common cutoff | Elevated: 16 µmol/L |
| NIH ODS, lower cutoffs also used | 12 to 14 µmol/L |
| NIH ODS, B12 sheet | Higher than 15 µmol/L |
| NIH ODS, for populations | 10 µmol/L (folate status in populations) |
| Cleveland Clinic | Around 5 to 15; mild 15 to 30; moderate 30 to 100; severe more than 100 µmol/L |
| Mayo Clinic Laboratories | Its own range for each age and sex, from birth to over 85 |
NIH ODS (Folate fact sheet, updated November 30, 2022): “A homocysteine cutoff of 10 micromol/L has been proposed for assessing folate status in populations” — a line for populations, which the checker shows beside every result and never counts. ODS’s Vitamin B12 fact sheet: “a serum homocysteine level higher than 15 micromol/L, for example, suggests vitamin B12 deficiency”, and then: “However, this indicator has poor specificity because it is influenced by other factors, such as low folate levels and, especially, by declines in kidney function”. Cleveland Clinic: “Some people have mild (15 to 30 mcmol/L) or moderate (30 to 100 mcmol/L) levels of homocysteine. More than 100 mcmol/L is a severe level.” Its bands share their ends, so a result of exactly 15 or 30 is shown on the line between two of them.
Mayo Clinic Laboratories’ range by age and sex
Mayo prints a range for every year of age from 3 to 85, and for the first three years in months. “Intervals are Mayo-derived, unless otherwise designated.” A selection of its rows, in nmol/mL (the same number as µmol/L); the checker uses the row for your exact age.
| Age | Female | Male |
|---|---|---|
| 0–11 months | 3.1–8.3 | 3.2–9.7 |
| 5 years | 3.4–8.1 | 3.5–9.4 |
| 10 years | 3.8–8.3 | 4.1–9.4 |
| 15 years | 4.2–8.9 | 5.0–9.8 |
| 18 years | 4.3–9.3 | 5.6–10.1 |
| 25 years | 4.4–10.4 | 6.3–11.3 |
| 30 years | 4.3–11.4 | 6.4–11.9 |
| 35 years | 4.5–12.2 | 6.4–12.6 |
| 40 years | 4.8–13.0 | 6.5–13.4 |
| 45 years | 4.9–13.9 | 6.6–14.2 |
| 50 years | 5.0–14.5 | 6.8–15.0 |
| 55 years | 5.2–15.0 | 6.9–15.7 |
| 60 years | 5.4–15.3 | 6.9–16.1 |
| 65 years | 5.6–15.6 | 7.1–16.3 |
| 70 years | 6.0–15.8 | 7.3–16.3 |
| 75 years | 6.5–15.9 | 7.3–16.3 |
| 80 years | 7.0–16.0 | 7.5–16.3 |
| over 85 years | 7.4–16.0 | 8.3–16.2 |
What moves it
Mayo Clinic Laboratories: “Other factors that may influence and increase serum homocysteine include: Age; Smoking; Poor diet/cofactor deficiencies; Chronic kidney disease/renal disease; Hypothyroidism”. “Medications that may increase homocysteine concentrations include: Methotrexate; Azuridine; Nitrous oxide; Phenytoin; Carbamazepine; Oral contraceptives”. MedlinePlus: “If your homocysteine levels are high, it doesn’t always mean you have a medical condition that needs treatment. Your results may be affected by: Your age. Homocysteine levels may get higher as you get older.; Your sex. Males usually have higher homocysteine levels than females, but levels in females increase after menopause.; Smoking.” Cleveland Clinic: “High homocysteine levels could mean you have a medical condition. But other factors can affect your homocysteine (Hcy) blood levels, including: Getting older; Being male or reaching menopause if you’re female; Using tobacco products”. MedlinePlus on a high result: “A high homocysteine level may be a sign that: You are not getting enough vitamin B12 or folic acid in your diet.; You (or your child) have homocystinuria. You will probably need more testing to rule out or confirm a diagnosis of homocystinuria.; You may have a higher risk of heart disease, stroke, or other blood vessel disorders.” “Higher than normal homocysteine levels may also happen with other conditions, such as osteoporosis, chronic kidney disease, hypothyroidism, schizophrenia, or Alzheimer’s disease or other types of dementia.”
B vitamins and the heart: what the trials found
NIH ODS: “An elevated homocysteine level has been associated with an increased risk of cardiovascular disease”. Then: “Folic acid (and vitamin B12) supplements lower homocysteine levels. However, these supplements do not actually decrease the risk of cardiovascular disease, although they appear to provide protection from stroke”. On the brain: “Despite this evidence, most clinical trial research has not shown that folic acid supplementation affects cognitive function or the development of dementia or Alzheimer’s disease, even though supplementation lowers homocysteine levels.” MedlinePlus: “Routine homocysteine testing to screen for heart disease risk isn’t recommended for everyone. That’s because it’s uncertain how much homocysteine levels affect heart and blood vessel diseases. Even though high levels of homocysteine can damage arteries, studies have shown that in most cases lowering homocysteine levels doesn’t reduce the risk of heart attack or stroke.” Mayo Clinic Laboratories: “Currently, the use of homocysteine for assessment of cardiovascular risk is uncertain and controversial.” “Based on several meta-analyses, at present, homocysteine may be regarded as a weak risk factor for coronary heart disease, and there is a lack of direct causal relationship between hyperhomocysteinemia and cardiovascular disease. It is most likely an indicator of poor lifestyle and diet.”
Read with B12, folate and MMA
Mayo Clinic Laboratories: “Measurement of methylmalonic acid (MMA) distinguishes between vitamin B12 (cobalamin) and folate deficiencies, as MMA is only elevated in vitamin B12 deficiency.” The Vitamin B12 Level Checker places a B12 and an MMA, and the Folate Level Checker a serum or red-cell folate.
Before the blood draw
MedlinePlus: “You may need to fast (not eat or drink) for 8-12 hours before a homocysteine test.” “Some medicines and supplements may affect your test results. So, tell your provider about all medicines and supplements you take, especially vitamin B. But don’t stop taking any medicines unless your provider tells you to.”
Worked examples
- 9 µmol/L, a woman of 45 (the page’s example): under all five high lines, inside Mayo’s 4.9–13.9 and Cleveland Clinic’s “around five to 15”.
- 13 µmol/L, a man of 30: over 1 of the 5 high lines — above Mayo’s 6.4–11.9 for his age, inside the 12 to 14 band of lower cutoffs, under 15 and 16.
- 15 µmol/L, a woman of 45: over 2 of the 5 — above Mayo’s 13.9 and the 12 to 14 band; not “higher than 15”; on the line between Cleveland Clinic’s “around five to 15” and its “mild”.
- 16 µmol/L, a man of 60: over 3 of the 5 — yet inside Mayo’s 6.9–16.1 for his age, and on ODS’s 16 cutoff, not over it.
- 3 µmol/L, a woman of 45: below Mayo’s range for her age; MedlinePlus: “Normally, your homocysteine levels are low.”
Common mistakes
- Reading one cutoff as the only one. ODS names 16, and 12 to 14 that “have also been used”; Mayo’s upper end runs from 8.1 for a girl of 5 to 16.3 for older men.
- Ignoring age and sex. MedlinePlus: “Homocysteine levels may get higher as you get older.” and “Males usually have higher homocysteine levels than females”.
- Treating nmol/mL as a different unit. It is the same number as µmol/L.
- Reading the 10 line as a personal line. ODS proposed it “for assessing folate status in populations”.
- Reading homocysteine without B12 and folate. ODS: it is “not a highly specific indicator of folate status”.
Frequently asked questions
What is a normal homocysteine level?
Cleveland Clinic: “In a healthy person, homocysteine levels are around five to 15 mcmol/L.” Mayo Clinic Laboratories prints a range for each age and sex, from 3.1–8.3 for a baby girl to 8.3–16.2 for a man over 85. Your lab’s printed range is the one your doctor uses.
What does a homocysteine blood test show?
MedlinePlus: “A homocysteine test measures the amount of homocysteine in a sample of your blood.” NIH ODS calls it “a commonly used functional indicator of folate status”, and adds that it is “not a highly specific indicator”.
What level of homocysteine is high?
NIH ODS: “The most commonly used cutoff value for elevated homocysteine levels is 16 micromol/L, although slightly lower values of 12 to 14 micromol/L have also been used”. Cleveland Clinic calls 15 to 30 “mild”, 30 to 100 “moderate” and over 100 “severe”. What a high result means for you is your doctor’s reading.
What causes high homocysteine?
Mayo Clinic Laboratories lists age, smoking, poor diet/cofactor deficiencies, chronic kidney disease and hypothyroidism, and six medicines. MedlinePlus adds that a high level “may be a sign that” a diet lacks vitamin B12 or folic acid, or of homocystinuria, and that “it doesn’t always mean you have a medical condition that needs treatment.”
Can homocysteine be too low?
MedlinePlus: “Normally, your homocysteine levels are low.” Mayo prints the lower end of its range for each age; a result under it is a question for your doctor. None of the sources here lists causes of a low result.
Do B vitamins lower homocysteine?
NIH ODS: “Folic acid (and vitamin B12) supplements lower homocysteine levels. However, these supplements do not actually decrease the risk of cardiovascular disease, although they appear to provide protection from stroke”. Cleveland Clinic: “But increasing your vitamin intake alone doesn’t reduce your risk of heart disease.” MedlinePlus: “If you have high homocysteine levels, your provider may suggest that you take vitamin supplements or make changes in the foods you eat.”
Do I need to fast for a homocysteine test?
MedlinePlus: “You may need to fast (not eat or drink) for 8-12 hours before a homocysteine test.”
Is µmol/L the same as nmol/mL?
Yes. Mayo Clinic Laboratories prints nmol/mL, NIH ODS micromol/L and Cleveland Clinic mcmol/L: a micromole per liter is a nanomole per milliliter, so 9 µmol/L is 9 nmol/mL.
More blood-test checkers: the Vitamin B12 Level Checker, the Folate Level Checker, the MCV Level Checker and the Ferritin Level Checker. Folate’s, B12’s and B6’s RDA and upper limit for your age: the Vitamin & Mineral Dose Lookup.
Read next
- Vitamin B9 — folate, the vitamin homocysteine is read with.
- Vitamin B12 as a nootropic
- Vitamin B6 as a nootropic — the third B vitamin MedlinePlus names.
- Folic acid for women and men
- Mind Lab Pro after 50 — B vitamins and age.
This is not medical advice, and nothing here diagnoses or treats anything. It shows where a number sits against published lines and quotes what the sources say about it; your lab’s own range, your B12 and folate, your kidneys, what you take, your history and your doctor decide what it means. Some links on this site are affiliate links: I buy what I review at full price, and a commission never changes a verdict.