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REMEDY : BNSSG referral pathways & Joint Formulary

Macrocytosis DRAFT

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Mean corpuscular volume >100fl

Potential causes:

  • Excess alcohol consumption
  • Liver disease
  • Medications (cytotoxics e.g. hydroxycarbamide; immunosuppressants e.g. azathioprine or certain anti-retroviral agents).
  • Reticulocytosis
  • B12 and /or folate deficiency
  • Presence of a monoclonal protein
  • Myelodysplastic syndrome (or other bone marrow disorders including myeloma)
  • Pregnancy can cause macrocytosis and Hb below the “normal range” (physiological not pathological): investigations only required if significant (MCV>108) or associated with anaemia (Hb<105 g/L) in the absence of iron deficiency.  Interpretation of B12 level in pregnancy (or the COCP) is uncertain, avoid testing unless clinical features strongly suggest B12 or folate deficiency
  • Hypothyroidism is a rare cause.

Please also see Remedy pages on B12 deficiency management and high B12

Who to refer

Refer for specialist opinion if any of the below red flags

In elderly, frail patients with an isolated macrocytosis (absence of cytopenias, haemolysis or myeloma) consider monitoring in the community or discussion with haematology rather than referral.

Vitamin B12 or folate deficiency does not normally require referral for haematology outpatient assessment. GI symptoms may need specialist assessment.

Red Flags

  • Suspected myelodysplastic syndrome (based on blood film report)
  • Other primary haematological cause suspected
  •  MCV > 100fl with accompanying cytopenia (excluding in B12 / folate deficiency)
  •  Persistent unexplained MCV > 105fl

Before referral

Investigations in Primary Care:

  • Alcohol history and appropriate lifestyle modification B12 and folate levels (consider sequential Intrinsic Factor antibodies and coeliac screen)
  • Blood film examination and reticulocyte count
  • Liver and thyroid function tests
  • Immunoglobulins and protein electrophoresis


URGENT ADVICE: 9am to 5pm via hospital switchboard for haematology SpR. ONLY for emergency advice. Out of hours and weekends – emergency advice may be obtained from the on call haematology clinician via hospital switchboard.

NON-URGENT ADVICE: use haematology advice and guidance service 

REFERRAL: through NHS e-referral system

Minimal information: the referral letter should include abnormal clinical findings (location, size, any associated features) and any abnormal full blood count results or other relevant test results, particularly if these investigations were not done in laboratories of the hospital to which the referral is made.