A high folate result on a blood test usually means you’re getting plenty of folate or folic acid, most often from a vitamin or fortified foods. It’s rarely dangerous on its own, but it’s worth one follow-up question: has your vitamin B12 been checked?

The short version

  • Most common reason: taking a prenatal vitamin, multivitamin, or folic acid pill, or eating a lot of fortified foods.
  • Timing matters: the standard blood test reflects what you’ve eaten or taken in the past few days, so a vitamin the morning of the test can raise the result.
  • The one to rule out: low vitamin B12 can cause folate to build up in the blood, and high folic acid intake can hide the signs of B12 deficiency.
  • Food folate isn’t the issue: there’s no upper limit for folate from regular food. The limit applies to folic acid from vitamins and fortified foods: 1,000 mcg a day for adults, according to the NIH.
  • If you’re pregnant, don’t stop your prenatal vitamin because of a high result. Talk with your provider first.

What the folate blood test measures

There are two kinds of folate blood tests, and they answer different questions. Your lab report should say which one you had.

Test What it reflects Affected by your last meal or vitamin?
Serum (or plasma) folate Your intake over the past few days Yes. A vitamin or fortified cereal shortly before the test can push it up.
Red blood cell (RBC) folate Your folate status over the past few months, when those blood cells were made Not much

The NIH describes serum folate above 3 ng/mL and red blood cell folate above 140 ng/mL as signs of adequate folate. There’s no single official cutoff for “too high.” Each lab sets its own reference range, so compare your number with the range printed on your report.

Because serum folate swings with recent intake, some labs ask you to fast before the test. If you took a vitamin or ate fortified cereal that morning, tell your provider; it may explain a high reading.

Common reasons folate runs high

1. Vitamins. This is the most common reason. The median prenatal vitamin contains 800 mcg of folate, according to the NIH, and many multivitamins contain 400 mcg or more. Taking two products that both contain folic acid, such as a prenatal and a separate folic acid pill, doubles up quickly.

2. Fortified foods. Enriched breads, pastas, and rice all contain added folic acid, and some breakfast cereals are fortified with 100% of the Daily Value in a single serving. These add up alongside a vitamin.

3. Timing of the test. A serum folate test taken soon after a vitamin or a fortified meal can read high even if your usual intake is reasonable.

4. Low vitamin B12. Your cells need B12 to use folate. When B12 is very low, folate can’t move into cells properly and builds up in the blood, according to clinical references such as the Columbia University health library. In that case, a high folate number means B12 needs attention. A folate test can’t diagnose B12 deficiency, so ask whether your B12 has been checked.

An MTHFR gene variant isn’t a reason folate reads high. The most common variant is linked to slightly lower blood folate on average, not higher, according to the CDC.

Is high folate harmful?

Folate from food isn’t known to cause harm, which is why there’s no upper limit for it. The questions are about folic acid from vitamins and fortified foods at high, sustained intakes. This summary of the research comes from the NIH’s review:

Concern What’s known
Hiding vitamin B12 deficiency Well established. High folic acid can correct the anemia of B12 deficiency while nerve damage continues. This is the main reason the 1,000 mcg upper limit exists.
Unmetabolized folic acid in the blood When intake is high, some folic acid circulates without being converted. Whether this has any health effect is still unclear.
Children’s development One study linked supplement intakes of 1,000 mcg or more around conception with lower scores on children’s thinking-skills tests at ages 4 to 5. It’s a single study and needs confirming.
Prostate cancer in men Some studies link folic acid supplements to a higher prostate cancer risk.

None of this means a high test result has hurt you. The goal is enough folic acid, and more doesn’t add protection.

High folate in pregnancy

A high reading during pregnancy most often reflects a prenatal vitamin doing its job. Don’t stop taking it on your own: folic acid protects against neural tube defects, and your folate needs stay higher for the whole pregnancy.

It is worth checking that you aren’t getting far more folic acid than you need. Going over the limit isn’t rare: in national survey data from the early 2000s, about a third of pregnant women got more supplemental folate than the upper limit, according to the NIH. The usual culprit is doubling up, such as a prenatal vitamin plus a separate folic acid pill plus highly fortified cereal.

The exception is a higher dose your doctor prescribed on purpose, such as 4,000 mcg a day after a pregnancy affected by a neural tube defect. Keep taking that as directed.

What to do next

Bring these questions to your provider:

  1. Which test was this, serum or red blood cell folate?
  2. Could a vitamin or meal before the test explain it?
  3. Has my vitamin B12 been checked?
  4. Adding up my vitamins and fortified foods, how much folic acid am I getting a day?
  5. Should I change anything, or is this expected with my prenatal vitamin?

Related reading

Sources

This article is for general information and is not a substitute for advice from your health care provider.