In poikilocytosis, erythrocytes have different shapes (rocket, pear, club, comma, etc).
Occurrence of spherocytes is a consequence of the primary defect in the red cell membrane. Spherocytes have increased thickness (about 3 µm), normal volume, and biconvex shape. Spheroidal cells appear in many types of haemolytic anemia, including hereditary spherocytosis and immune haemolytic anemia, and in burns.
Erythrocytes of oval or elliptical shape as a result of a defect in the red cell membrane, most likely a disturbance of the structure and constituents of spectrin. Such cells can be found in blood of patients with hereditary elliptocytosis, and sometimes in myelofibrosis. Artefacts are common and should be excluded.
Leptocytes are erythrocytes of normal volume but very reduced thickness. They have peripheral ring zones but there is an increase in hemoglobin in the central part.
Acanthocytes are red cells with fine projections from the surface (“spiky” cells). They may be found in patients with inherited decrease or complete deficiency of -lipoproteins (abetalipoproteinemia), or with neurological diseases.
Megalocytes have increased longitudinal diameter, thickness, and volume, and are hypochromic. They can be observed in all megaloblastoses due to B12 deficiency.
Poikilocytosis describes variations in the shape of erythrocytes. Erythrocytes of different shapes are present in the same blood smear. Poikilocytosis is always accompanied by anisocytosis.
These erythrocytes have a sickle shape, i.e., the shape of half-moon. They are characteristic for cases of hereditary hemolytic anemia-drepanocytosis (sickle-cell anemia). Drepanocytosis is characterized by crises with great pains (vaso-exclusive crises) caused by the obstruction of blood vessels with rigid sickled red cells.