Synopsis
Confirm folate deficiency, identify dietary, malabsorptive, medicine-related or increased-demand causes, exclude vitamin B12 deficiency safely and deliver replacement with documented response and prevention of recurrence.
- Folate deficiency produces ineffective megaloblastic erythropoiesis, often with macro-ovalocytes, hypersegmented neutrophils and low reticulocytes, but mixed iron deficiency can leave MCV within range.
- Assess diet, alcohol, coeliac and other small-bowel disease, pregnancy, chronic haemolysis, dialysis and medicines that antagonise folate metabolism or alter absorption.
- Measure vitamin B12 before or alongside folate and assess neurological symptoms explicitly. Do not give folic acid alone when B12 deficiency remains plausible.
Key red flags
Paraesthesia, proprioceptive loss, gait disturbance, cognitive change, gastric surgery or autoimmune history makes folate-only treatment unsafe and B12 assessment urgent.
Investigation priorities
Define severity and recognise ineffective megaloblastic production.
Management branches
Macrocytosis, megaloblastic film change, cytopenia or risk factors suggest folate deficiency.
- Take FBC, film, reticulocytes, serum folate, B12, ferritin, liver and thyroid tests, and ask specifically about neurological symptoms, diet, alcohol, pregnancy, bowel disease and medicines.
- The preferred interpretation requires biochemical deficiency plus a compatible phenotype and cause; an alternative mixed-deficiency pathway uses RDW, film and all haematinics when MCV is normal.
Key medicines
Folic acidFor folate-deficient megaloblastic anaemia, give 5 mg by mouth once daily for 4 months; continue longer while the underlying cause remains active.
Folic acid in severe malabsorptionThe BNF allows up to 15 mg by mouth daily in malabsorption; select the dose with specialist review and monitor clinical and haematological response.