Folate (vitamin B9) is needed for cell division, DNA synthesis and the formation of red blood cells. It is especially important where cells divide fast — in the bone marrow and in the fetus.
Folate deficiency, like B12 deficiency, causes a particular anemia and raises homocysteine — a vascular risk factor.
Reference ranges
Approximate reference for serum folate:
| Normal | > 4 ng/mL |
| Deficiency | < 3 ng/mL |
| More accurate | red-cell folate reflects stores over months |
What an elevated level means
A high folate is usually not dangerous — the excess is excreted. It occurs with supplements and fortified foods.
An important nuance: large doses of folic acid can mask B12 deficiency (they normalize the blood but do not protect the nerves). So they are not taken uncontrolled without checking B12.
What a low level means
Folate deficiency shows up as anemia (fatigue, weakness, pallor), and also as irritability and reduced appetite.
Causes: little greenery and vegetables in the diet, alcohol abuse, pregnancy (increased need), malabsorption, some medications.
Special importance: folate deficiency in early pregnancy raises the risk of neural tube defects in the fetus — which is why it is prescribed in advance when planning a pregnancy.
How the test is done
Venous blood, fasting. Do not take folic acid supplements before the test, so as not to inflate the result.
With deficiency, vitamin B12 is always checked — their deficiencies often go together and are treated differently.
What affects the value
- Greens and vegetables — the main source of folate; a lack leads to deficiency.
- Alcohol — worsens absorption and stores.
- Pregnancy — sharply increases the need.
- Some medications — methotrexate and others lower the level.
- Bowel diseases — impair absorption.
Calculate using this marker
Calculators where Folic acid (vitamin B9) is used directly:
Frequently asked questions
Why is folic acid needed in pregnancy?
It is critically important for the proper formation of the fetal neural tube in early pregnancy. Its deficiency raises the risk of developmental defects. So folate is recommended starting when planning a pregnancy, before conception.
Can folic acid be taken without tests?
Preventive doses when planning a pregnancy — yes, on a doctor's advice. But large doses can mask vitamin B12 deficiency (they fix the blood but not the nerves), so uncontrolled high doses are not taken.
How are folate, B12 and homocysteine linked?
Both folate and B12 are needed to process homocysteine. With a deficiency of either, homocysteine rises — and that is a vascular risk factor. So these markers are often assessed together.