• Anisocytosis: this is a variation in size of RBCs
• Macrocytosis: large RBCs that may be due to a vitamin B12 or folate deficiency. They are seen in pernicious anemia, chronic alcoholism, and megaloblastic anemia.
• Microcytosis: this is the presence of small RBCs that may be due to an iron deficiency anemia or to an inherited disorder such as thalassemia.

• Acanthrocytes (spur, thorn or spiculated cells): irregular shaped cells with 5-10 spicules. May be present in the blood of post splenectomy patients and in chronic alcoholism.
• Echinocytes (burr, crenated or berry cells): may have 10-30 spiny projections and often seen in patients with renal failure or iron deficiency. May be an artifact – something caused during sample preparation.
• Elliptocytes (ovalocyte): elliptical-shaped RBC seen in hereditary elliptocytosis and various anemias.
• Keratocyte (horn cell): A half-moon or spindle shaped RBC that may be seen in patients with disseminated intravascular coagulation (DIC) or a vascular prosthesis.
• Rouleaux: RBCs that appear as a stack of coins and seen in patients with multiple myeloma or macroglobulinemia.
• Sickle cells: crescent shape RBCs that are characteristic of sickle cell anemia.
• Target cells (leptocytes or codocytes): RBCs that resemble a bull's-eye. Commonly seen in patients with hemoglobinopathies (abnormal inherited forms of hemoglobin), thalassemia and various anemias.
• Teardrop cells (dacrocytes): RBCs that resemble a teardrop. Often seen in patients with myelofibrosis and thalassemia.
• Schistocytes: fragments or broken pieces of RBCs. This may be due to a disorder that is causing the red blood cells to be especially fragile or due to mechanical hemolysis as seen sometimes with devices such as artificial heart valves, or in severely burned patients.
• Spherocytosis: sphere-shaped RBCs that are often present in hereditary spherocytosis or due to an immune hemolytic anemia.
• Spicule (crenated): scalloped or serrated perimeter due to loss of water from the cell or to liver disease.

• Hypochromasia: this may be seen in a variety of disorders including thalassemia and iron deficiency. The RBC is pale in color due to insufficient hemoglobin and contains a large, hollow middle (central pallor) of the cell.
• Hyperchromasia: the RBC is darker in color that normal; this may be due to dehydration.
• Polychromasia: blue-staining RBCs, indicating that they are immature due to early release from the bone marrow.

• Nucleated RBCs (normoblasts): a very immature form of RBCs seen when there is a severe demand for RBCs to be released by the bone marrow. May be seen in severe anemia, myelofibrosis, thalassemia, miliary tuberculosis, cancers that involve the bone marrow, and in chronic hypoxemia (low oxygen levels). Nucleated RBCs can be normal in infants for a short time after birth.
• Reticulocytes: these are immature RBCs that are usually polychromatic in color. A few of these young red blood cells are normal in the circulation. Elevated numbers may be seen with acute blood loss, hypoxia, RBC destruction, sickle cell disease, glucose-6-phosphate dehydrogenase (G6PD) deficiency, and autoimmune hemolytic anemia.
• Siderocyte, sideroblast, ringed sideroblast: When RBCs are stained with Prussian blue dye, iron granules may be seen. Sideroblasts are immature siderocytes and may actually for a ring pattern indicative of sideroblastic anemia.
• Basophilic stippling (dark blue dots inside the RBC): due to the precipitation of nuclear material (ribosomes) and may be present in heavy metal poisoning (such as lead), nutritional deficiencies, or myelofibrosis.
• Heinz bodies: large inclusion bodies (granules) in the RBCs when stained with crystal violet. May be due to an enzyme (G6PD) deficiency, unstable hemoglobin variant, thalassemia, and autoimmune hemolytic anemia.
• Howell-Jolly bodies (small round remnants of nuclear DNA inside cell): present in sickle cell anemia, hemolytic or megaloblastic anemias, and may be seen after a splenectomy.
• Cabot’s Rings: threadlike inclusions that form a ring within the RBC. May be seen in a variety of anemias.

Malarial parasites: Patients with malaria may have these parasites living inside RBCs, breaking them apart as they leave. This is not a routine finding; it would normally only be detected on a blood smear when an investigating doctor suspects that a patient has an active case of malaria.