A target cell (codocyte, Mexican hat cell) is a peripheral red blood cell of adult humans with central staining from precipitated haemoglobin seen in in blood film in conditions such as:
- Sickle cell disease
- Iron deficiency anaemia
- Cirrhosis and other liver disease
- Haemoglobin C disease
The term leptocyte can be used when the target appearance is only partial. These cells all have a disproportional increase in the ratio of surface membrane area to volume compared to normal erythrocytes. This relative membrane excess is due to either increased red cell surface area or decreased intracellular haemoglobin content. Such cells are less osmotically fragile that normal RBCs.