B12 Deficiency

Haematinic deficiency is the most common cause of anaemia. Iron deficiency (see BMS15) is more common than B12 or folate deficiency. B12 and folate cause a macrocytic appearance (large red cells, raised MCV) and can also cause in severe cases a low white cell and platelet count. The appearances are often missed in mild cases as they can be mild and overlap with normal morphology.

In very severe cses the film can be markedly abnormal with pancytopenia and red cell fragmentation. In severe cases,  B12 deficiency has been confused for both haematological malignancies and for thrombotic throbocytopenic purpura. 

In patients with a macrocytic anaemia the red cells are larger than the lymphocytes and you will be able to see oval macrocytes. There may also be some tear drop cells although these should raise the possibility of myelofibrosis rather than B12 deficiency.

The most useful diagnostic feature from a morphology perspective is hyper segmented neutrophils. These are strongly suggestive of B12 deficiency as they are not a feature of other haematologicl disorders. Normal neutrophils have 3-5 lobes and you may see 6 lobes occasionally in normal neutrophils. 7 or more lobes in neutrophils is strongly suggestive of B12 or folate deficiency and if these are seen then a comment to check the B12 and folate status in the film report is appropriate.