Red cell folate

Ranges vary widely between laboratory methods (some print 285 to 1500 nmol/L, others 160 to 640 ug/L); use the range your lab printed.

Red cell folate is the amount of folate stored inside the red blood cells, which is taken up while the cells are being made and stays with them for their four-month life. It therefore reflects folate supply over the previous few months rather than the last few days, in the way that HbA1c does for glucose. Most laboratories now use serum folate instead because it is easier to measure reliably.

Doctors request it when a serum folate is near the limit of the range or when a recent change in diet or a supplement might have made the serum folate misleading, and in some hospital settings when looking into large red cells. Many laboratories no longer offer it.

• Folic acid supplements taken over several months
• A diet consistently rich in folate

• A diet low in folate over several months
• Alcohol excess
• Poor absorption, including coeliac disease
• Pregnancy
• Some medicines, including methotrexate and some anticonvulsants
• Vitamin B12 shortage, because folate cannot get into the cells properly

• A low value with a normal serum folate is common when vitamin B12 is short, and corrects once B12 is replaced
• Different laboratory methods give very different numbers and the test is harder to standardise than serum folate
• A recent blood transfusion changes it

No fasting needed. EDTA tube; the laboratory needs the haematocrit from the same sample to calculate it.

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