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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Folate deficiency

Haematology and transfusion · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Escalate

Severe symptomatic anaemia, haemodynamic compromise, pancytopenia with bleeding or infection, pregnancy with significant illness, or neurological features suggesting concurrent vitamin B12 deficiency requires urgent senior assessment. Take pretreatment folate and B12 samples where feasible, but do not delay B12 replacement when neurological injury is suspected; folic acid alone is unsafe in that setting.

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.
  • Serum folate reflects recent intake and should be interpreted with the clinical and blood-film phenotype. A low result does not explain why deficiency developed.
  • Usual adult treatment for folate-deficient megaloblastic anaemia is folic acid 5 mg by mouth daily for 4 months; longer treatment is needed when the cause persists.
  • Severe malabsorption may require a higher oral dose under the BNF and specialist plan. Apparent failure should prompt adherence, diagnosis, ongoing demand and intestinal disease review.
  • In chronic haemolytic states, prophylactic folate may be indicated through the disease-specific haematology pathway because sustained reticulocyte production increases requirement.
  • A reticulocyte and haemoglobin response supports effective replacement, but recurrence prevention requires dietary support, treatment of malabsorption and coordinated medicine review.

Key red flags

Possible concurrent B12 disease

Paraesthesia, proprioceptive loss, gait disturbance, cognitive change, gastric surgery or autoimmune history makes folate-only treatment unsafe and B12 assessment urgent.

Investigation priorities

01
FBC, film and absolute reticulocytesFirst step

Define severity and recognise ineffective megaloblastic production.

Management branches

Confirm safelyEstablish deficiency and protect against B12 harm

Macrocytosis, megaloblastic film change, cytopenia or risk factors suggest folate deficiency.

  1. 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.
  2. 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.
  3. Escalate neurological findings for prompt B12 treatment and severe symptomatic anaemia, bleeding, infection or pancytopenia for urgent clinical and haematology assessment.

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.Exclude or treat vitamin B12 deficiency first because folate can improve the blood count while neurological injury progresses. Review methotrexate, trimethoprim and antiseizure interactions with the responsible clinician.
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.Do not escalate solely for a slow FBC without revisiting adherence, diagnosis, B12 and iron status, continued demand and intestinal disease. Long-term high dosing needs a clear indication.
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • BNF folic acid monographAdult treatment dose, duration, malabsorption dosing and prescribing cautions.
  • NICE NG239 vitamin B12 recommendationsRecognition and prompt management of concurrent B12-related neurological disease.
  • NHS vitamin B12 or folate deficiency anaemiaUK symptoms, causes, treatment course and complications.
  • NICE coeliac disease recommendationsTesting pathway for a treatable malabsorptive cause.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom