Sickle Information and Courses from MediaLab, Inc.

This photograph of a peripheral blood smear from an 18-year-old North African woman with anemia reveals sickle cells. Target cells are not conspicuous. This shifts the diagnostic evidence away from HbSC disease. Cells tagged by arrows are variants of sickle cells. These may appear when multiple abnormal hemoglobin combinations are responsible for the clinical problem. The cell marked by the single arrow is an envelope formed not only in HbS disease but in HbC disease as well. Two arrows tag a blister cell, which, when seen in several fields, should prompt a hemoglobin electrophoresis to determine the presence of an undiagnosed hemoglobinopathy. Blister cells with fuzzy edged pseudo-vacuoles (see photo) are to be distinguished from the pseudo-vacuoles (blister)with razor sharp edges suggesting a microangiopathic state.

The patient whose blood smear is shown in the photograph was a 32-year-old female from Virginia who came to the high country of Colorado to ski. The day after arrival, she experienced shortness of breath, fatigue, and upper abdominal pain. She was seen in a medical center in the mountains where a working diagnosis of altitude sickness was made. A CBC revealed RBCs 5.1 x 1012/L, hemoglobin 12.8g/dL, MCV 60fL, hematocrit 40.9%, and normal total WBC, differential, and platelet count. The RDW was normal. Further questioning revealed a previous diagnosis of heterozygous beta-chain thalassemia. No other abnormal hemoglobins were found on hemoglobin electrophoresis, but HbA-2 was elevated to 5%, supporting the diagnosis of beta thalassemia. The patient's poikylocytosis and anisocytosis may be a clue to an underlying erythrocyte abnormality. Persons with iron deficiency anemia may experience various degrees of hypoxia upon arriving at high altitudes. Those with sickle cell disease and thalassemia minor (as in this case) may experience bone pain or other symptoms of "crisis" and/or alteration in the appearance of their erythrocytes upon sudden high altitude exposure. The classic teaching is that in differentiating iron deficiency anemia from thalassemia, increased RDW would favor iron deficiency; normal RDW favors thalassemia.

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.

The synonym for a drepanocyte is a sickle cell.

Drepanocytes or sickle cells are formed as a result of the presence of hemoglobin S in the red cell. As the red cell ages, it becomes less flexible or deformable and becomes rigid as it passes through the low oxygen tension atmosphere of the small capillaries in the body. In the absence of oxygen, hemoglobin S polymerizes into rods, causing the sickle cell shape. Sickle cells can be somewhat pointed at the ends, as the cell shown in the center, or more rounded or cigar-shaped, as the one slightly to the left. Several sickle cells are indicated by S, and a target cell or dacrocyte is indicated by T in the smear shown on the right.

Several drepanocytes are also seen in this field of a blood smear from a sickle cell patient. Sickle cells may have either the appearance shown in the photomicrograph at S, with sharp points, or may appear with more blunted ends, as in D. Homozygous sickle cell anemia is the condition in which drepanocytes are seen; however other tests are needed to make the diagnosis of sickle cell anemia. Most sickled cells can revert back to the discoid shape when oxygenated. About 10% of sickled cells are unable to revert back to their original shape after repeated sickling episodes.