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Eeva-RiittaSavolainen

Macrocytosis (Increased MCV)

Mean corpuscular volume or MCV denotes the average red blood cell volume. The normal reference range for MCV is 82-98 fl (femtolitres). Macrocytosis is the condition where the average red blood cell size exceeds the upper limit of the reference range.
MCV is measured with an automatic cell counter either by the so-called impedance principle (also known as the Coulter principle) or based on light scattering.
Macrocytosis may be evenly distributed (i.e. the size of all red blood cells is increased), or the size may be increased in only a proportion of the cells (e.g. reticulocytes found in association with accelerated erythropoiesis).
In most laboratories the MCV value is reported automatically together with haemoglobin values without specific order. Values higher than the upper limit of the reference value (98 fl) are quite common.

If a patient has anaemia, haematological investigations are carried out as usual Megaloblastic Anaemia Assessment of Anaemia in Adults.
If the haemoglobin level is normal:
1. Alcoholism and alcohol abuse are the most common causes of macrocytosis. If past history and the clinical impression make ethanol a likely cause, no other investigations are required but the situation is explained to the patient. An attempt is made to reduce alcohol consumption through counselling Brief Interventions for Risky Use of Alcohol. A reduction or a complete stop in alcohol intake is not reflected in the MCV value until after several months.
2. If heavy alcohol intake is not probable, additional investigations are carried out. Reticulocytosis associated with macrocytosis may be a sign of haemolysis or of accelerated erythropoiesis due to bleeding. The possibility of megaloblastic anaemia is investigated by measurement of serum active vitamin B₁₂ and folate. Hypothyroidism should be excluded. Bone marrow examination Bone Marrow Examination is not justified unless the patient's symptoms and pathological findings in the blood picture (e.g. cytopenias) suggest a malignant blood disease (e.g. myelodysplastic syndrome Myelodysplastic Syndromes (MDS)). The cause of a mild macrocytosis quite often remains unclear.