Ovalocytes are rod shaped erythrocytes with nearly parallel lateral walls.

If the long axis of an erythrocyte is no more than twice as long as the short axis, the cell is an ovalocyte.

If the long axis is more than twice as long as the short axis, the cell is an elliptocyte.

• Hemoglobin tends to collect at each end of these cells.
• The ends of the cells are rounded and never pointed, to be differentated from sickle cells.
• Ovalocytes present in greater than 25% of red cells on the blood smear are characteristic of hereditary ovalocytosis. The oval shape is attributed to a defect in horizontal red cell membrane protein interactions.
• Lesser numbers of circulating ovalocytes may be present in various anemias including megaloblastic, sideroblastic, iron deficiency, and in thalassemias.
• A rare ovalocyte (less than 1%) may be found on almost any peripheral blood smear.
• Resistance to malarial infection may be a beneficial attribute of hereditary ovalocytosis.