Folate, Red Blood Cell
Measures the folate stored inside your red blood cells. It reflects your folate status over roughly the past three to four months.
AI-drafted. Awaiting verificationAlso called RBC folate, RCFLOINC 2283-0
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What it is
Folate is vitamin B9. Your body uses it to make DNA and to build new red blood cells. Folate gets built into red blood cells as they form in the bone marrow and stays there for the cell's lifetime, about 120 days. This test measures the folate in those cells, so it shows your average folate status over the past few months. A serum folate test, by comparison, can change after a single meal or supplement.
Why it matters
Folate is needed for cell growth, and low levels can lead to an anemia with unusually large red blood cells (megaloblastic anemia). Folate also matters before and in early pregnancy, because enough folate lowers the chance of neural tube defects in the baby. Red blood cell folate is a steadier measure of long-term status than serum folate, and it is the measure used for neural tube defect thresholds. Low red blood cell folate can also happen when vitamin B12 is low, so clinicians often look at both.
If it’s low
A low red blood cell folate level means your folate stores have been low for a few months. It can come from low intake, poor absorption, higher needs such as pregnancy, or low vitamin B12. If it stays low, it can contribute to anemia with large red blood cells.
Common causes
- Eating few leafy greens, beans or fortified grains
- Regular heavy alcohol use
- Conditions that reduce absorption, such as celiac disease or inflammatory bowel disease
- Pregnancy and breastfeeding, which raise folate needs
- Some medicines, including methotrexate and some anti-seizure drugs
- Low vitamin B12, which can also lower red blood cell folate
- Conditions with fast red blood cell turnover, such as hemolytic anemia
What can help
- Talk with your clinician about whether a folic acid or folate supplement is right for you
- Eat folate-rich foods such as leafy greens, beans, lentils, citrus and fortified grains
- Ask whether your vitamin B12 should be checked before low folate is treated
If it’s high
A high red blood cell folate level usually comes from folic acid or multivitamin supplements, or from a diet with fortified grains, leafy greens and beans. High levels are not usually a concern by themselves. Folic acid can improve the anemia caused by low vitamin B12 while leaving nerve problems untreated, so clinicians like to know your B12 level too.
Common causes
- Folic acid or multivitamin supplements
- Regular intake of fortified grains and cereals
- A diet rich in leafy greens, beans and citrus
- Differences in lab method, since assays vary widely
What can help
- Share your supplement list with your clinician
- Ask whether your vitamin B12 level should be checked too
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: 280 and above ng/mL. Source: Quest Diagnostics, American Journal of Clinical Nutrition.
- Adults (this one applies)280 and above ng/mL
Sources: Quest Diagnostics, American Journal of Clinical Nutrition
See RBC Folate by age and sex, with the U.S. survey numbers where they exist.
Wellness targets
Narrower ranges some clinicians aim for. Being outside one doesn’t mean something is wrong.
906 and above nmol/L (Women, 12–49). Evidence: Moderate. Irish population data found neural tube defects in fewer than 8 per 10,000 pregnancies when red blood cell folate was 906 nmol/L (400 ng/mL) or higher, and modelling of Chinese trial data agreed, with risk falling further above about 1,000 nmol/L. WHO uses 906 nmol/L as its population threshold for women of reproductive age. It is a population target, not a personal treatment goal.
Red blood cell folate deficiency cutoff (hematologic indicator, microbiologic assay)
- Below the folate-deficiency cutoffbelow 305 nmol/L
- At or above the cutoff305 and above nmol/L
WHO neural tube defect prevention threshold (women of reproductive age)
- Below the neural tube defect prevention thresholdbelow 906 nmol/L
- At or above the threshold906 and above nmol/L
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 RBC Folate by age and sex: every percentile as a table, with a download.
What can affect your result
- Folate and folic acid intake from food, fortified foods and supplements over the past 3 to 4 months
- Vitamin B12 status
- Pregnancy, alcohol use and conditions that reduce absorption
- Assay method: results vary more between RBC folate assays than between serum folate assays
- A recent blood transfusion
- Low vitamin B12 can lower red blood cell folate, because B12 is needed for red cells to keep folate, so a low result can reflect either vitamin.
- Assays differ a lot. A 2015 College of American Pathologists proficiency survey found much larger differences between platforms for RBC folate than for serum folate, so cutoffs from one assay may not fit another.
- A recent red blood cell transfusion means part of the sample comes from donor cells.
- High-dose biotin supplements can interfere with some immunoassays, so ask your lab whether to pause biotin before the draw.
Any time of day. About 3 to 4 months. Red blood cell folate reflects folate status over the preceding 120 days, so it moves slowly after a change in diet or supplements.
When to talk to a clinician
See a clinician if a low result comes with unusual tiredness, shortness of breath, pale skin or a sore tongue. If you could become pregnant, ask your clinician about folic acid supplements now rather than waiting for a test result.
Questions you could ask
- Does my folate level matter for a pregnancy I am planning or for any medicines I take?
- Should my vitamin B12 level be checked too?
- Is my supplement still the right one for me?
- Could low vitamin B12 be part of this?
- What is the best way to raise it, and when should we recheck?
Questions people ask
What is the difference between serum folate and red blood cell folate?
Serum folate reflects recent intake and can change after a meal or supplement. Red blood cell folate reflects about the past 3 to 4 months. Many clinicians prefer it for long-term status, though it is ordered less often and varies more between labs.
Why does my lab's cutoff differ from the WHO numbers?
Labs often print an adequacy limit. Quest's is above 280 ng/mL, about 634 nmol/L. A commonly used deficiency cutoff is lower, 305 nmol/L (about 135 ng/mL), and the WHO neural tube defect threshold for women of reproductive age is higher, 906 nmol/L (about 400 ng/mL).
How do I convert ng/mL to nmol/L?
Multiply ng/mL by 2.266, so 400 ng/mL is about 906 nmol/L. To go the other way, multiply nmol/L by 0.4414.
Show the science and sources
Units
- 1 ng/mL = 1 ng/mL
- 1 ng/mL = 2.266 nmol/L
Open the RBC Folate unit converter
Is a change real?
RBC Folate naturally varies about 12% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 37% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Desirable Biological Variation Database specifications, 2014 update (Minchinela J, Ricos C, et al.; the 'Ricos database', a compilation of median published CVI/CVG).
For clinicians and researchers
RBC folate accumulates during erythropoiesis, mostly as polyglutamate forms of 5-methyl-tetrahydrofolate, and is retained for the roughly 120-day cell lifespan. It is considered an index of tissue stores and long-term folate status. Methods include the microbiologic assay (Lactobacillus rhamnosus, historically the reference approach), automated competitive protein-binding and immunoassays used by most clinical labs, and LC-MS/MS. Whole-blood hemolysates need deconjugation of polyglutamates before measurement, and the value is corrected for hematocrit, which contributes to poorer agreement between RBC folate assays than between serum folate assays. Cutoffs are assay-specific: the commonly used deficiency cutoff of below 305 nmol/L (hematologic indicator, set where hypersegmented neutrophils appeared in folate-depletion studies) comes mainly from microbiologic-assay data, while the older cutoff of below 340 nmol/L (homocysteine-based) came from the Bio-Rad radioassay, and applying a cutoff to a different assay misclassifies status. In Irish data, neural tube defect prevalence was below 8 per 10,000 at RBC folate of 906 nmol/L or higher, and modelling of Chinese trial data suggested about 1,000 to 1,300 nmol/L for optimal prevention. Because B12 is needed to retain folate in developing red cells, low RBC folate can reflect B12 deficiency as well as folate deficiency. To convert, 1 ng/mL = 2.266 nmol/L (folic acid basis, MW 441.4).
LOINC 2283-0 (primary), 14731-4. Specimen: red-blood-cells.
Sources
- Folate, RBC (test details as listed by Fullscript), Quest Diagnostics
- Applying inappropriate cutoffs leads to misinterpretation of folate status in the US population, American Journal of Clinical Nutrition (2016)
- Guideline: optimal serum and red blood cell folate concentrations in women of reproductive age for prevention of neural tube defects, World Health Organization (2015)
- Biomarkers of Nutrition for Development (BOND): Folate Review, Journal of Nutrition (2015)
- Revisiting the hematological manifestations of vitamin B12 deficiency, Frontiers in Nutrition (2026)
- Folic acid (PubChem CID 135398658), NIH National Library of Medicine (PubChem)
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.