Folate (Folic Acid)
Folate· also: Folic Acid, Serum Folate, RBC Folate
Clinical Overview
Folate (vitamin B9) is a water-soluble B vitamin essential for DNA synthesis, cell division, and amino acid metabolism. It is especially critical during rapid cell division in embryonic development — folate deficiency in early pregnancy is a leading cause of neural tube defects (spina bifida, anencephaly). Folate is found in leafy green vegetables, legumes, fortified cereals, and liver.
Why This Test Matters
Folate deficiency causes megaloblastic anemia and neural tube defects. Unlike B12 deficiency, folate deficiency does not cause neurological damage. Red cell folate (measured in red blood cells rather than serum) is a better marker of long-term folate status than serum folate, which reflects recent dietary intake. All women of childbearing age should take 400 µg/day of folic acid starting at least 1 month before conception to prevent neural tube defects.
Reference RangesWHO/IFCC standards
| Reference Range | Unit | Notes |
|---|---|---|
| 2 – 20 | ng/mL | — |
Also reported in: nmol/L.
Critical (Panic) Values
Critical Low: < 2 ng/mL. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High Folate Causes
- Folic acid supplementation (most common)
- High folate diet
Low Folate Causes
- Poor dietary intake (especially in elderly, alcoholics, or food insecure populations)
- Alcohol excess (reduces absorption and increases folate excretion)
- Malabsorption (celiac disease, inflammatory bowel disease)
- Pregnancy and lactation (increased demand)
- Hemolytic anemia (increased turnover)
- Hemodialysis (folate loss)
- Medications: methotrexate (folate antagonist), phenytoin, trimethoprim, pyrimethamine
Signs & Symptoms to Watch For
How to Prepare for This Test
No fasting required for serum folate (reflects recent intake). Red blood cell folate requires standard blood draw. Avoid folic acid supplements for 24–48 hours before serum folate testing if measuring baseline status.
Factors That Can Affect Results
- Recent dietary intake (a single high-folate meal normalizes serum folate transiently)
- Hemolysis (red cells contain 40× more folate than serum — hemolysis falsely raises serum folate)
- Vitamin B12 deficiency can deplete RBC folate (secondary folate deficiency)
Related Topics
Frequently Asked Questions
Why is folic acid recommended before pregnancy?
The neural tube (which becomes the brain and spinal cord) closes within 28 days of conception — often before a woman knows she is pregnant. Folate is required for this closure. Supplementation must begin at least 1 month before conception to ensure adequate levels during the critical window. Women with a previous neural tube defect pregnancy or on anticonvulsants need higher doses (4–5 mg/day) under medical supervision.
Can high folate levels mask B12 deficiency?
Yes. This is an important clinical concern. High folate supplementation can correct the megaloblastic anemia of B12 deficiency without correcting the B12 deficiency itself. The neurological complications of B12 deficiency (subacute combined degeneration) continue to progress silently. For this reason, B12 levels should always be checked alongside folate before starting high-dose folic acid supplementation.