Red cells: Target cells

Codocytes, more commonly known as target cells have an area of increased staining which would usually appear 'empty' as it is the area of central pallor. This gives the cells a characteristic bullseye / target like appearance, hence the name. In vivo they are bell shaped and get flattened during the smearing process so appear as targets on the blood film. The codocytes can be microcytic, normocytic or even macrocytic and this depends on the underlying abnormality. They are formed as a result of there being redundant membrane in relation to the volume of cytoplasm. In conditions where there is excess red cell membrane (obstructive jaundice for example) target cells are formed due to excess membrane lipid. In ion deficiency, thalassaemias or haemoglobinopathies, the red cell cytoplasmic volume decreases without the proportionate reduction in the membrane.

Target cells can be caused by a range of different things:

• Haemoglobinopathies

• Thalassaemias

• Anaemia (such as sideroblastic, or iron deficiency)

• Liver disease

• Obstructive jaundice

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Image from personal photography.