Codocyte

Codocytes, also known as target cells, are red blood cells that have the appearance of a target with a bullseye. The cells have a dark center surrounded by a white ring and dark outer layer causing the cells to look similar to a target. Such cells are thin and have a disproportional increase in the surface membrane area to volume ratio. This increased ratio may result from an increase in membrane surface area or a decrease in hemoglobin content. Morphologically, target cells have a central, hemoglobinized area surrounded by an area of pallor. The periphery of the cell contains a band of hemoglobin.

Diseases causing target cells
Cells may appear in association with the following conditions:
 * Liver disease: Lecithin cholesterol acyltransferase (LCAT) activity may be decreased in obstructive liver disease. Decreased enzymatic activity increases the cholesterol to phospholipid ratio, producing an absolute increase in surface area of the red blood cell membranes.
 * Iron deficiency: Decrease in hemoglobin content relative to surface area is probably the reason for the appearance of target cells. This is also seen in Thalassemias, Hemoglobin C disease, etc.
 * Thalassemia (hemoglobinopathy)
 * Hemoglobin C Disease
 * Post-splenectomy: A major function of the spleen is the clearance of opsonized, deformed, and damaged erythrocytes by splenic macrophages. If splenic macrophage function is abnormal or absent because of splenectomy, altered erythrocytes will not be removed from the circulation efficiently. Therefore, increased numbers of target cells may be observed.
 * Autosplenectomy caused by sickle cell anemia