Folate is present in leafy vegetables and fruit but is destroyed by overcooking. It is not stored in the body and so dietary deficiency is very common. Folate and iron are absorbed in the jejunum so combined deficiency is very suggestive of coeliac disease or inflammatory bowel disease. The most useful investigation is dietary history.

Causes of low serum folate levels:

• insufficient/poor diet
• malabsorption syndromes syndromes (e.g. gastric resection/bypass, coeliac disease, Crohn’s disease, pancreatic insufficiency and gut infection e.g. giardiasis, fishtapeworm)
• chronic alcoholism
• pregnancy
• dialysis
• drug treatment (anticonvulsants, colestyramine, sulfasalazine, methotrexate)
• increased cell turnover (haemolysis, haemglobinopathy, exfoliative skin disease)

• Macrocytosis +/- anaemia
• Pancytopenia
• Suspected dietary deficiency
• Malabsorption syndromes
• Pre-dialysis testing

Tiredness is not an indication for testing.

Cautions for serum folate testing interpretation:

• Low serum folate levels may represent true deficiency or may be secondary to acute illness. Consider full clinical context, other haematological parameters (haemolysis, unexplained anaemia, raised MCV) and evidence of any underlying causes (see above).
• Results should be considered in conjunction with any concurrent B12 deficiency results.
• High serum folate levels are of no clinical significance and are likely to reflect dietary intake.

Red cell folate is no longer offered as a test by most laboratories.

• Tests should not be repeated within 1 month of previous test, repeat testing should be based around development of any of above indications.
• Initial assessment of response to oral folate replacement at 1 month.

Devalia V, Hamilton MS, Molloy AM, on behalf of the British Committee for Standards in Haematology. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. British Journal of Haematology 2014 166(4): 496-513 Free full text