Folate (Vitamin B9), Serum
Measures folate (vitamin B9) in your blood. It mostly reflects what you ate recently, and it helps explain anemia and low folate intake.
AI-drafted. Awaiting verificationAlso called B9, Vit B9LOINC 2284-8
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What it is
Folate, also called vitamin B9, helps your body make DNA and new red blood cells. It comes from leafy green vegetables, fruits and liver. Folic acid is the form added to fortified foods such as enriched bread and cereal, and it is the form in most supplements. This test measures the folate circulating in your blood serum. It rises and falls with what you have eaten in the last few days, so it shows your recent intake more than your long-term stores.
Why it matters
Your body needs folate to build DNA and healthy red blood cells, so it matters most when cells are dividing quickly, such as in pregnancy. Too little can cause a type of anemia with large red blood cells, which can bring tiredness, weakness and shortness of breath. Getting enough folic acid before and in early pregnancy helps lower the chance of neural tube defects such as spina bifida. Low B12 can cause a similar anemia, so clinicians often check both together.
If it’s low
A low result means there is less folate in your blood than your lab expects. It usually reflects a few weeks of low folate intake, or a body that needs more than it is getting. It doesn't prove that you are anemic. If it stays low, if you have anemia, or if you are pregnant, your clinician may look further. They may check B12, and sometimes red blood cell folate, which reflects longer-term stores.
Common causes
- Eating few vegetables, fruits and fortified foods
- Heavy or long-term alcohol use
- Pregnancy and breastfeeding, when the body needs more folate
- Digestive conditions that reduce absorption, such as celiac disease, Crohn's disease or ulcerative colitis
- Certain medicines, including some anti-seizure medicines, sulfasalazine and methotrexate
- Dialysis, and conditions that speed up blood-cell production or cell growth
What can help
- Ask your clinician what is behind the low result and whether B12 should be checked too, because folate alone can hide a B12 problem
- Include folate-rich foods such as leafy greens, beans, citrus fruit and liver, and foods fortified with folic acid such as enriched bread, pasta and cereal
- If you could become pregnant, ask your clinician about folic acid before pregnancy
- Ask whether alcohol or any medicines you take could be playing a part, and don't stop any medicine on your own
If it’s high
A high folate result is common and usually isn't a problem on its own. It most often means you recently took a supplement or ate fortified foods, especially if you weren't fasting. Where flour is fortified with folic acid, high values are not unusual. One reason clinicians still look at it is that high folic acid intake can cover up the blood-count signs of low vitamin B12, so they like to make sure B12 isn't low.
Common causes
- Folic acid or multivitamin supplements, including prenatal vitamins
- Fortified foods such as enriched bread, pasta, rice and breakfast cereal
- A sample taken soon after a meal or a supplement
- Low vitamin B12, which can make folate build up in the blood
- A damaged blood sample (hemolysis), because red blood cells are rich in folate
What can help
- Tell your clinician about every supplement you take, including prenatal vitamins and B-complex products
- Ask whether your B12 has been checked, if it hasn't
- If you are pregnant or planning pregnancy, talk with your clinician before changing any supplement
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 3 and above ng/mL. Source: Labcorp, MedlinePlus (National Library of Medicine).
- Adults (this one applies)3 and above ng/mL
Sources: Labcorp, MedlinePlus (National Library of Medicine)
See Folate by age and sex, with the U.S. survey numbers where they exist.
WHO folate-deficiency cutoff for populations (2005 technical consultation)
- Below the folate-deficiency cutoffbelow 10 nmol/L
- At or above the cutoff10 and above nmol/L
Early WHO serum folate categories (1972, historical)
- Clinical deficiencybelow 3 ng/mL
- Marginal3 to under 6 ng/mL
- Normal (6 ng/mL or higher)6 and above ng/mL
If this applies to you
Folate means a little more for some people. Open the one that fits you.
Had weight-loss surgery
Folate can run low after surgery, partly from eating fewer folate-rich foods or missing multivitamins. ASMBS suggests checking it in everyone, with particular attention for women who could become pregnant.
Celiac disease or IBD
Folate is on ACG's list of other tests that may be part of celiac follow-up, and on BSG's list for people with IBD at risk of malnutrition. Low folate is one of the other causes of anemia BSG asks clinicians to consider in IBD.
Hemochromatosis or iron overload
EASL advises checking folate from time to time in people with hemochromatosis, especially those who need many phlebotomies.
Low iron or anemia
Low folate can also cause anemia. BSG notes that it can hide the small-cell pattern of low iron and is one of the reasons iron treatment may not seem to work.
Vegan or vegetarian
Plant-rich diets are high in folate, and a 2016 review notes that blood folate tends to be high in vegetarians. Folate can correct the blood-count signs of low B12 but not its effects on nerves, the Institute of Medicine notes, which is why B12 is checked on its own.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Folate by age and sex: every percentile as a table, with a download.
What can affect your result
- Recent meals and supplements: serum folate follows what you ate in the last few hours to days
- Hemolysis (damaged blood cells) falsely raises the result
- Pregnancy and breastfeeding raise the body's folate needs
- Alcohol, and some medicines, can lower folate
- Fortification: where flour is fortified with folic acid, low serum folate has become uncommon
- Assay method: folate assays aren't well standardized, so results can differ between methods and labs
- Sample handling: folate is the least stable B vitamin, so light, warmth and delays before processing can affect the result
- Eating, or taking folic acid or a multivitamin, shortly before the draw raises serum folate. Overnight-fasted and recently fed samples differ by about 10% on average, which is why a fasting sample is recommended.
- Hemolysis (damaged blood cells in the tube) falsely raises the result, because red blood cells hold far more folate than serum does. Some labs reject hemolyzed samples.
- High-dose biotin supplements can interfere with some immunoassays; Labcorp advises stopping biotin at least 72 hours before the draw, so check with your clinician or lab first.
- Methotrexate and leucovorin (folinic acid) can cross-react with the folate-binding protein used in some assays and give misleading results.
- MedlinePlus lists medicines that can lower folate measurements, including alcohol, birth control pills, estrogens, phenytoin, phenobarbital, methotrexate and some antibiotics.
Morning, after an overnight fast, when possible. Moves quickly. A recent meal or supplement can raise it within hours, and a few weeks of low intake can lower it. Red blood cell folate is the slower measure and reflects roughly the past 3 to 4 months.
When to talk to a clinician
Talk with a clinician if your folate is below your lab's range, or below about 3 ng/mL (about 7 nmol/L), the traditional deficiency cutoff, particularly with unusual tiredness, weakness, shortness of breath, pale skin or a sore tongue. If you are pregnant or planning pregnancy, bring up a low result soon. If your B12 hasn't been checked, ask about it, especially if you have numbness, tingling or balance problems, which folate does not fix.
Questions you could ask
- Do my symptoms, my blood counts (such as MCV) and my folate result fit together?
- Should this be rechecked, and if so, when?
- Could my supplements or fortified foods explain this result?
- Has my B12 been checked?
- What do you think is behind my low folate?
- Should we also check B12, and would a red blood cell folate test help?
Questions people ask
Should I get serum folate or red blood cell folate?
They answer different questions. Serum folate shows your recent intake and can change within days to weeks. Red blood cell folate reflects about the past 3 to 4 months and is considered a better measure of tissue stores. It is also the measure linked to neural tube defect risk. Your clinician decides which one to order, and sometimes both.
Why do ranges for folate differ between labs and websites?
Folate assays aren't well standardized, so different methods give different numbers. Labcorp lists above 3.0 ng/mL, while MedlinePlus gives 2.7–17.0 ng/mL. Where food is fortified with folic acid, average folate levels are much higher than they used to be, and some labs only report a lower limit.
How do I convert ng/mL to nmol/L?
Multiply ng/mL by 2.266 to get nmol/L, so 3 ng/mL is about 6.8 nmol/L. To go the other way, multiply nmol/L by 0.4414. Some labs print µg/L, which is the same number as ng/mL.
Does a high folate result mean I'm taking too much?
Not usually. High results most often reflect supplements, a multivitamin or fortified foods, especially if you weren't fasting. Folate from food has no set upper limit. Folic acid from supplements and fortified foods does have one for adults, so it is fair to ask your clinician whether your supplements match what you need.
If my folate is low, should I just start a folic acid supplement?
Talk with your clinician first. Low B12 can cause a similar anemia, and folic acid can improve the blood counts of low B12 while nerve problems keep getting worse. Clinicians usually check B12 at the same time so that the right problem is treated. The right amount also depends on your situation, including pregnancy.
Show the science and sources
Units
- 1 ng/mL = 1 ng/mL
- 1 ng/mL = 2.266 nmol/L
Open the Folate unit converter
Is a change real?
Folate naturally varies about 10.7% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 32% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Biological variation of plasma 25-hydroxyvitamin D3, serum vitamin B12, folate and ferritin in Turkish healthy subjects (Ozkanay H et al.).
For clinicians and researchers
Serum or plasma folate is mostly 5-methyltetrahydrofolate monoglutamate and reflects recent intake. It falls within about three weeks of a folate-depleted diet, before red blood cell folate falls and before megaloblastic changes appear (Herbert's classic depletion study, summarized by Shane 2011). Red blood cell folate reflects the preceding ~120 days. Clinical laboratories use automated competitive protein-binding assays (Labcorp lists an electrochemiluminescence immunoassay). Protein-binding assays vary between kits, typically give lower values than the microbiological (Lactobacillus) assay, and historically measured about 2–20 ng/mL, so some labs report a '>' upper limit. The 1960s–70s cutoffs came from microbiological-assay studies and the WHO 2005 cutoffs from NHANES III Bio-Rad radioassay data, so neither transfers exactly to current automated assays. Hemolysis falsely raises serum results; methotrexate and leucovorin cross-react with the binding protein; biotin can interfere with streptavidin-based assays; and fasting versus recently fed samples differ by about 10%. Cutoffs: the WHO 2005 technical consultation (as cited by BOND) recommends serum folate below 10 nmol/L (about 4.4 ng/mL) and red blood cell folate below 340 nmol/L for population-level deficiency, derived from a homocysteine-based metabolic indicator in NHANES III; the older negative-balance threshold was below 7 nmol/L (3 ng/mL); and 1972 WHO categories were below 3 ng/mL (deficient), 3–6 (marginal) and 6–20 (normal). Red blood cell folate of about 906 nmol/L (400 ng/mL) or higher in women of reproductive age is associated with the lowest neural tube defect risk. BOND concludes that single indices are inadequate on their own, and red blood cell folate and homocysteine complement serum folate. In vitamin B12 deficiency, folate becomes trapped as 5-methyltetrahydrofolate (the methyl trap), which can produce a functional intracellular folate deficiency alongside normal or falsely high serum folate that falls after B12 replacement. The US adult upper intake level is 1,000 µg/day of folic acid and none exists for food folate; the limit is based on cases in which folic acid corrected the anemia of B12 deficiency without reversing neurologic damage. Prevalence of serum folate below 10 nmol/L in the US fell from 24% before fortification to 1% or less afterward.
LOINC 2284-8 (primary), 14732-2, 35210-4. Specimen: serum.
Sources
- Folate (Folic Acid) (test 002014), Labcorp
- Folic acid - test, MedlinePlus (National Library of Medicine) (2025)
- Biomarkers of Nutrition for Development—Folate Review, The Journal of Nutrition (2015)
- Folate status assessment history: implications for measurement of biomarkers in NHANES, The American Journal of Clinical Nutrition (2011)
- Folic Acid (molecular weight 441.4 g/mol), PubChem (National Library of Medicine)
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.