HNY Policy and Pathway Repository - North Yorkshire

The most common cause of a high MCV is alcohol excess, however other causes should be considered.

None provided

Differential diagnosis:

• Artefact - e.g. delayed sample processing or cold haemagglutinins.
• Physiological - mild macrocytosis can be normal in pregnancy (approx. 4fl rise from baseline).
• Reticulocytosis - reticulocytes are ~25% larger than normal RBC. High count suggests a marrow response to red cell destruction or blood loss.
• Excess alcohol intake - target cells or stomatocytes on a blood film report suggests alcohol excess or liver dysfunction.
• Abnormal liver function - often anaemic and low platelets if advanced.
• Hypothyroidism - can also give a normocytic anaemia
• Vitamin B12 or folate deficiency - hypersegmented neutrophils and / or oval macrocytes on a blood film report suggest a megaloblastic anaemia.
• Drugs e.g. hydroxycarbamide, azathioprine and many chemotherapy agents. Can give the appearances of a megaloblastic anaemia.
• Bone marrow disorder, e.g. myelodysplastic syndrome - blood film may be suggestive and may also have leucopenia or thrombocytopenia.

Baseline investigations:

• Repeat FBC (ensure sample gets to laboratory on same day), blood film, reticulocytes, LFT, TFT, B12 / folate.
• Note that a mild reduction in vitamin B12 levels can be seen as an artefact in pregnancy, women taking COC / HRT, or with metformin. There is also significant overlap in vitamin B12 levels between those with true deficiency and those with a level at the lower end of the normal range. A trial of therapy may be necessary- the MCV should normalise in 3 months if due to B12 deficiency.

Vitamin B12 / folate:

NICE have produced a very useful Clinical Knowledge Summary. https://cks.nice.org.uk/anaemia-b12-and-folate-deficiency 

Referral:

• Further management / referral based on suspected cause.
• Consider haematology referral if suspected red cell haemolysis or bone marrow disorder.
• We do not see patients with an unexplained macrocytosis but an otherwise normal blood count.

Haematology Handbook - South Tees Hospitals NHS Foundation Trust

• South Tees Hospitals