Folate (vitamin B9) is an essential B vitamin required for DNA synthesis, cell division and the production of red blood cells. It is particularly critical during early pregnancy, where adequate levels prevent neural tube defects in the developing fetus.
Folate deficiency is common worldwide — more common than many patients expect — and its symptoms often overlap with other conditions, making it easy to miss without a blood test. Here's what the test measures and what to do if your result is low.
What does the blood test measure?
The serum folate test measures circulating folate at the time of the blood draw. It reflects recent dietary intake and can fall quickly with a poor diet. Red cell folate (erythrocyte folate) is a more stable marker that reflects the folate stored in red blood cells — a better indicator of longer-term status but less commonly ordered.
Reference ranges vary slightly between labs, but as a general guide, serum folate below 7 nmol/L (3 µg/L) is considered deficient. Values between 7 and 10 nmol/L may be borderline.
Causes of folate deficiency
- Poor dietary intake — folate is found in green leafy vegetables, legumes, citrus fruit and fortified cereals
- Malabsorption — coeliac disease, inflammatory bowel disease, short bowel syndrome
- Increased demand — pregnancy, haemolytic anaemia, rapid cell turnover
- Medications — methotrexate, trimethoprim, some anticonvulsants (phenytoin, carbamazepine)
- Alcohol excess — impairs folate absorption and increases urinary excretion
- Kidney dialysis — folate is lost during the process
Symptoms of folate deficiency
- Fatigue and weakness
- Pale skin
- Mouth ulcers and a sore, red tongue (glossitis)
- Irritability, difficulty concentrating
- In severe cases: macrocytic anaemia (enlarged red blood cells that carry oxygen poorly)
Folate and vitamin B12: an important relationship
Folate and vitamin B12 deficiency produce very similar blood pictures — both cause macrocytic anaemia. It's essential to test both simultaneously: treating folate deficiency without diagnosing concurrent B12 deficiency can mask neurological damage from B12 deficiency that folate treatment won't correct. Our guide to vitamin B12 deficiency covers the B12 side of this pairing in detail.
Treatment
Folate deficiency is treated with folic acid supplements, typically 5 mg daily for four months. Food sources can be increased alongside supplementation: dark green vegetables (spinach, kale, broccoli), beans and lentils, oranges and fortified cereals.
During pregnancy (or when planning a pregnancy), folic acid 400 µg daily is recommended from at least one month before conception through the first trimester — increasing to 5 mg daily for women with risk factors including diabetes, a family history of neural tube defects or use of anticonvulsants.