Folate is the quieter half of a pair. When a blood count suggests a particular kind of anemia, two vitamins usually get tested at the same time, and B12 is the one people have heard of.
MedlinePlus, in its Medical Encyclopedia entry "Folic acid – test" (review/update date 3 February 2025), states the purpose plainly: "This test is done to check for folic acid deficiency."
The reason it is so often ordered alongside B12 is that the two produce a similar picture on the blood count, and the report on its own does not separate them.
Why the CBC raises the question
Folate, like B12, is involved in making new cells. When the bone marrow is short of what it needs to build red cells properly, the cells that reach the bloodstream can be affected, and one visible consequence on a blood count is that the average cell size runs large.
MedlinePlus's "RBC indices" page (review/update 27 February 2026) defines MCV as "Average red blood cell size" and gives its normal range as 79 to 95 femtoliters, adding that "Normal value ranges may vary slightly among different labs."
MedlinePlus's folate page connects the two directly, noting that testing may be conducted for anemia potentially caused by folate deficiency, or for megaloblastic anemia arising from low folic acid or vitamin B12.
That last phrase is the entire reason the two are tested together. The blood count says the picture is consistent with either. The vitamin levels are what distinguish them, and it is possible for both to be involved at once. The types of anemia covers the broader classification that cell size feeds into.
The numbers
MedlinePlus gives the reference figures directly: "The normal range is 2.7 to 17.0 nanograms per milliliter (ng/mL) or 6.12 to 38.52 nanomoles per liter (nmol/L)."
It follows with the caveat that appears on almost every MedlinePlus lab page and deserves more attention than it gets: "Normal value ranges may vary slightly among different labs."
This matters practically. Folate is measured in different ways, results are reported in different units, and the interval printed on your report is the one your laboratory established for its own method. Comparing your figure to a number you read somewhere else is comparing two things that were not built to be compared, and why your lab's reference range is different sets out where those intervals actually come from.
If your result sits just outside the interval, that is worth reading in context rather than in isolation. An abnormal blood test when you feel fine explains why reference intervals are constructed so that a proportion of entirely healthy people fall outside them.
What a low result can mean, per MedlinePlus
The page states that lower-than-normal levels may indicate poor diet, malabsorption syndrome such as celiac disease, or malnutrition.
Three items, and it is worth noticing that they are not the same kind of thing.
Intake. How much folate is arriving.
Absorption. Whether what arrives is taken up. Celiac disease is named specifically, and it is a condition affecting the gut's ability to absorb rather than a dietary shortfall.
Overall nutritional state. Malnutrition is a broader condition of which a low folate is one visible marker rather than the whole story.
Those three lead to entirely different investigations and entirely different answers, which is the reason a low result is the beginning of a question rather than the end of one. A general recommendation aimed at intake does nothing for a reader whose problem is absorption, and they may reasonably believe they have addressed something they have not.
Folate and B12 together, and why the order matters
There is a reason clinicians are careful about the sequence when both are being considered, and it is worth knowing that the care exists even though the detail belongs to them.
MedlinePlus's "Vitamin B12 level" page (review/update 10 January 2026) describes B12 deficiency as having a nervous system dimension alongside the blood one, listing numbness or tingling in the arms and legs, weakness and loss of balance among what a low level can cause. Its blood effects and folate's blood effects overlap; its nerve effects are its own.
That asymmetry is exactly why neither vitamin is treated on the basis of a blood count alone, and why this site publishes no supplement, no dose and no regimen for either of them. What is safe and appropriate depends on which deficiency is present, whether both are, what caused it, and what else is going on, and none of that is knowable from a number.
If you have had both tested and are waiting on results, that is the normal sequence rather than a sign that something complicated was found.
Pregnancy, mentioned carefully
Folate comes up in pregnancy more than in any other context, and this page is going to be deliberately brief about it.
Folate status is monitored during pregnancy, and pregnancy is one of the situations in which a clinician actively tracks it. What that monitoring means for any individual, and what if anything follows from it, is a conversation with the clinician providing that care and not something a general article should shape.
What this site can usefully cover is how the blood count itself behaves in pregnancy, because the reference intervals themselves shift and a result read against the wrong interval causes unnecessary alarm. CBC normal values in pregnancy covers that.
What this page will not do
No dose, no supplement recommendation, no food list, no target level to aim for.
The reason is the same one this site applies across the anemia cluster and stated first on its iron studies page: acting on a number without knowing the mechanism behind it is a way to feel you have handled something you have not. The cause determines the response, and the cause is established by a clinician with the whole picture.
What is publishable is what the named source says, quoted and dated, which is above.
The short version
- MedlinePlus (3 February 2025) states the test is done to check for folic acid deficiency.
- It is usually ordered alongside B12 because the two produce a similar picture on a blood count, and both can be involved.
- The normal range MedlinePlus gives is 2.7 to 17.0 ng/mL, with the note that ranges vary between labs.
- Low results may indicate poor diet, malabsorption such as celiac disease, or malnutrition. Those are three different problems.
- A low result opens an investigation rather than closing one.
- No dose or supplement is recommended here. That belongs to the clinician who ordered the test. How to read a CBC report will help you find the relevant lines before that conversation, and why your hemoglobin might be low covers the wider set of explanations.
