Folic Acid Test: Normal Levels, Deficiency & Risks

Understanding Folic Acid (Vitamin B9 / Folate)

I recall a young woman who came to my clinic complaining of persistent fatigue and a sore tongue. She was a vegetarian on a limited diet. Her blood work showed a low folate level. Within weeks of starting folic acid supplements, her energy returned and her symptoms resolved. This is a classic presentation of folate deficiency — a condition that is both common and easily treatable.

Folic acid, also known as vitamin B9 or folate, is a water-soluble B vitamin that plays a critical role in DNA synthesis, red blood cell production, and homocysteine metabolism. Your body cannot produce it, so you must obtain it from food (leafy greens, legumes, fortified grains) or supplements. The laboratory test measures folate in your blood, usually in the serum or plasma, and helps identify deficiencies or toxicities.

Why is the Folate Blood Test Done?

In my experience, the main reasons to check folate levels include:

• Unexplained anaemia, especially macrocytic anaemia (large red blood cells)
• Fatigue, weakness, shortness of breath
• Gastrointestinal symptoms like diarrhoea or mouth ulcers
• Neurological issues such as numbness, tingling, or cognitive changes
• Evaluating nutritional status in pregnant women, alcoholics, or those with malabsorption disorders (e.g., coeliac disease, Crohn’s)
• Monitoring therapy with methotrexate or other antifolate drugs

Reference Ranges for Folate

These are typical reference intervals for serum folate. Laboratories may vary slightly, so always interpret with your specific lab’s normal range.

Note: Red blood cell (RBC) folate is a more stable measure of long-term status, but serum folate is commonly used for initial screening.

What is the LOINC code for Folic Acid?

The internationally recognised LOINC (Logical Observation Identifiers Names and Codes) for folic acid in serum or plasma is 14629-0 (Folic acid [Mass/volume] in Serum or Plasma).

Low Folate: What Does It Mean?

Low serum folate typically indicates a deficiency. Common causes include:

• Inadequate dietary intake (especially in vegans, elderly, or those with poor appetite)
• Alcoholism (alcohol impairs folate absorption and increases excretion)
• Malabsorption (coeliac disease, inflammatory bowel disease, gastric bypass)
• Increased demand (pregnancy, lactation, haemolytic anaemia, cancer)
• Medications like methotrexate, sulfasalazine, antiepileptics (phenytoin, phenobarbital)

Symptoms of deficiency include fatigue, megaloblastic anaemia, glossitis (smooth, red tongue), irritability, and, in severe cases, neural tube defects in a developing fetus. If you have a low result, your doctor will often suggest supplements (400–1000 mcg daily) and dietary changes.

Is high folate dangerous?

My patients sometimes worry when their folate comes back high. Fortunately, because folic acid is water-soluble, excess is usually excreted in urine and toxicity is rare. High levels can occur with:

• Taking high-dose supplements (>1 mg daily)
• Consuming heavily fortified foods
• Severe vitamin B12 deficiency (in which case folate can mask B12 deficiency anaemia)

Persistently high folate may also be seen in some cancers or chronic diseases as a marker of cell turnover, but this is not a standalone diagnostic sign. If your level is elevated, your doctor will consider your overall clinical picture.

Folate during pregnancy

One of the most critical times to ensure adequate folate is during early pregnancy. I cannot emphasise enough the importance of taking 400–800 mcg of folic acid daily from at least one month before conception through the first trimester. This reduces the risk of neural tube defects (spina bifida, anencephaly) by up to 70%. The NHS recommends all women planning a pregnancy take a daily folic acid supplement. Women with a previous NTD or on certain medications may need a higher dose (4–5 mg).

How to prepare for the folate test?

Fasting is usually not required, but your doctor may recommend a light meal. Some labs prefer you avoid biotin supplements for 24 hours, as high-dose biotin can interfere with the assay. Always inform your doctor about all medications and supplements you take.

Treatment and Prevention of Folate Deficiency

If you are diagnosed with low folate, the standard treatment is oral folic acid supplementation (400–1000 mcg daily for mild deficiency, higher doses for severe cases or pregnancy). Dietary sources include dark leafy greens (spinach, kale), legumes, asparagus, Brussels sprouts, orange juice, and fortified cereals. In my practice, I also check vitamin B12 levels because a combined deficiency is common, and treating low folate without B12 can mask progression of B12 deficiency neuropathy.

Prevention is straightforward for most people: a balanced diet rich in folate-containing foods, and prenatal vitamins for women of childbearing age.

Frequently Asked Questions