Dimorphism refers to the presence of two distinct population of red cells on the blood film. When using the term, it is important to describe the two as it may be important for the differential diagnosis. Things to consider when describing the different red cell populations would be the size of the cells, their shape and their haemoglobin content.

A dimorphic blood film picture may be seen in a range of different conditions. Examples include:

• Transfusion
• Sideroblastic anaemia
• Anaemia undergoing treatment
• Delayed transfusion reaction
• Chimaerism as a result of a bone marrow transplant

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Images from personal photography.