Folate (Serum) Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Folate?

Folate (vitamin B9) is a water-soluble B vitamin essential for DNA synthesis, cell division, and amino acid metabolism. The term 'folate' refers to the naturally occurring forms found in food, while 'folic acid' is the synthetic form used in supplements and food fortification.

Folate works closely with vitamin B12 in a metabolic cycle that converts homocysteine to methionine. When either folate or B12 is deficient, homocysteine accumulates — an independent risk factor for cardiovascular disease. Folate is also critical for neural tube development in early pregnancy, which is why the NHS recommends folic acid supplementation before conception and during the first trimester.

Serum folate reflects recent dietary intake (the last few days to weeks), while red cell folate provides a longer-term picture (2–4 months). Most UK laboratories now measure serum folate as the first-line test.

Why Is Folate Tested?

• Anaemia investigation — folate deficiency causes megaloblastic anaemia (large, immature red blood cells)
• Pregnancy planning — adequate folate prevents neural tube defects such as spina bifida
• Elevated homocysteine — folate and B12 are the primary regulators of homocysteine levels
• Neurological symptoms — tingling, numbness, cognitive changes can indicate B12 or folate deficiency
• Malabsorption screening — coeliac disease and inflammatory bowel disease impair folate absorption
• Medication monitoring — methotrexate, phenytoin, and trimethoprim interfere with folate metabolism

Normal Ranges

Serum folate can fluctuate with recent meals. A fasting sample provides the most reliable result.

What Do High Folate Levels Mean?

• Supplementation — the most common cause; folic acid supplements rapidly raise serum folate
• Fortified foods — breakfast cereals and bread flour in some countries are fortified with folic acid
• Vitamin B12 deficiency — paradoxically, folate may appear normal or high while B12 is low, masking megaloblastic anaemia
• Bacterial overgrowth — some gut bacteria synthesise folate, raising levels
• Kidney disease — reduced excretion can elevate folate

What Do Low Folate Levels Mean?

• Inadequate dietary intake — poor diet lacking green leafy vegetables, legumes, and fortified foods
• Alcohol excess — alcohol impairs folate absorption and increases urinary excretion
• Coeliac disease — damage to the jejunum (where folate is absorbed) causes deficiency
• Inflammatory bowel disease — Crohn's disease particularly affects the small intestine
• Pregnancy — increased folate demands for rapid cell division
• Medications — methotrexate (folate antagonist), phenytoin, trimethoprim, oral contraceptives
• Haemolytic anaemia — increased red cell turnover depletes folate stores

How to Improve Your Folate Levels

• Eat folate-rich foods — dark leafy greens (spinach, kale, broccoli), lentils, chickpeas, asparagus, avocado, Brussels sprouts
• Consider supplementation — 400 µg folic acid daily is recommended for all women planning pregnancy; higher doses (5 mg) for those with previous neural tube defect-affected pregnancies
• Reduce alcohol intake — even moderate drinking can impair folate status
• Check for coeliac disease — if folate is persistently low despite good diet, coeliac screening is warranted
• Cook carefully — folate is heat-sensitive; lightly steam rather than boil vegetables
• Check B12 simultaneously — folate and B12 work together; supplementing one without checking the other can mask deficiency

When Should You Get Tested?

• You have symptoms of anaemia (fatigue, pallor, shortness of breath)
• You are planning pregnancy or in early pregnancy
• You have coeliac disease or IBD
• You take methotrexate, phenytoin, or other folate-depleting medications
• You consume alcohol regularly

Which Lola Health Tests Include Folate?

Serum folate is included in Vital Check and Peak Insights panels. Available as an add-on with any Lola Health blood test. For best results, pair with vitamin B12 and a full blood count.