How should I assess folate deficiency?
Q - How do you treat a patient with an isolated folate deficiency and macrocytosis but normal haemoglobin?
A - A low red cell folate is unequivocal evidence of folate deficiency and is a consequence of several months' reduced supply. Serum folate levels reflect recent dietary intake, therefore are of limited diagnostic value.
Assuming the red cell folate is reduced in this case, the likely cause is a reduced dietary intake often in association with other factors such as alcoholism, chronic
ill-health or pregnancy.
Additional causes are drugs, malabsorption or excessive utilisation due to malignancy or chronic, well-compensated haemolysis. The latter may be present even with a normal haemoglobin.
A clinical history should be taken with particular reference to diet, drugs, alcohol intake and symptoms of malabsorption.
Additional investigations should include a blood film, reticulocyte count and Hb electrophoresis together with liver function tests. Nutritional status should be assessed with measurement of other haematinics, if not already performed. Testing for anti-endomysial antibodies may detect patients with subclinical coeliac disease. If these tests are unrewarding, the patient should be referred for a specialist investigation.
Treatment should be with oral folic acid 5-15mg/day for four months. As the Hb is normal, it may take some time for the MCV to correct, reflecting the normal 120-day red cell turnover. At the same time, patients should be encouraged to increase their dietary intake. It is important that vitamin B12 levels are normal, as treatment with folic acid can precipitate neuropathy in patients with B12 deficiency. The need for maintenance therapy will depend on the cause.
Kate Ryan is consultant haematologist, North West London Hospitals Trust