Macrocytic anaemia.

Macrocytosis of red cells is now more easily and precisely detected in the laboratory by the adoption of electronic methods of cell volume measurement. This means the practitioner will be more frequently faced with the problem of what an elevated mean corpuscular volume (MCV) means. Macrocytic anaemia is not synonymous with folate or cobalamin deficiency, there being many causes of non-megaloblastic macrocytosis including excess alcohol, hypothyroidism, and liver disease. The commonest cause is blood regeneration as after a bleed, or in response to a haematinic or in haemolysis, as reticulocytes are large red cells and will raise the MCV. Megaloblastic anaemia, as in folate or cobalamin deficiency, has a normal or low reticulocyte count and a multiplicity of causes which must be identified as the cause may require treatment in its own right as well as the prescription of the required vitamin.