Folate

Laboratories vary in both limits (lower limits of 2.5 to 4 and upper limits of 18 to 27 ug/L are all in use) and many print nmol/L; use the range your lab printed.

Folate is a B vitamin (B9) needed to make DNA and therefore new cells, including red blood cells. It comes from green vegetables, pulses, fortified cereals and liver, and the body's stores last only a few months. Serum folate reflects recent intake over the last few days to weeks, so it moves quickly with diet.

Doctors request it alongside vitamin B12 when the red cells are large or the haemoglobin is low, in people with poor diet, alcohol excess, coeliac disease or on medicines that interfere with folate, and before and during pregnancy planning.

• Folic acid supplements and fortified foods
• A recent meal rich in folate
• Vitamin B12 shortage, because folate is not being used
• Some bowel conditions where bacteria make folate

• A diet low in green vegetables and pulses
• Alcohol excess
• Poor absorption, including coeliac disease and Crohn's disease
• Pregnancy and breastfeeding, because demand rises
• Some medicines, including methotrexate, some anticonvulsants, trimethoprim and sulfasalazine
• Conditions where cells turn over quickly, such as red cell breakdown and some skin conditions
• Kidney dialysis

• A single low value reflects the last few days' diet and can be normal on repeat
• A haemolysed sample reads high, because red cells contain much more folate than serum
• A sample left for a long time before analysis reads low
• A recent supplement or fortified breakfast cereal raises it
• Different laboratory methods give different numbers

Ideally fasting, before any supplements, and the sample protected from delay and light. Read with vitamin B12 and a full blood count.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.