A peripheral blood smear from a patient presenting with recurrent episodes of severe pain and anemia is shown above. What is the most likely diagnosis?
A. Iron deficiency anemia
B. Thalassemia major
C. Hereditary spherocytosis
D. Sickle cell anemia
Explanation
Image Findings
Numerous sickle-shaped red blood cells (drepanocytes) are prominently visible throughout the field.
Presence of target cells (codocytes), characterized by a central area of hemoglobin surrounded by a pale ring, and then an outer ring of hemoglobin.
Significant anisocytosis (variation in red cell size) and poikilocytosis (variation in red cell shape).
A nucleated red blood cell (NRBC) is visible (indicated by the red line in some crops), indicating increased erythropoietic activity.
A polymorphonuclear leukocyte (neutrophil) is also present.
Diagnosis
Key Point
The presence of numerous sickle cells is pathognomonic for sickle cell anemia.
Sickle cell anemia is a genetic disorder characterized by the presence of an abnormal hemoglobin, hemoglobin S (HbS). Under conditions of deoxygenation, HbS polymerizes, leading to the distortion of red blood cells into a rigid, sickle shape. These sickle cells are fragile, leading to chronic hemolytic anemia, and can obstruct microvasculature, causing vaso-occlusive crises, which manifest as severe pain.
Patients with sickle cell anemia often present with chronic hemolytic anemia, recurrent painful vaso-occlusive crises, acute chest syndrome, splenic sequestration, and increased susceptibility to infections (especially encapsulated organisms due to functional asplenia).
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The most characteristic finding on a peripheral smear for sickle cell disease is the presence of sickle cells (drepanocytes). Other common findings include target cells, nucleated red blood cells, and Howell-Jolly bodies (due to functional asplenia).
Key Point
Solubility tests (e.g., Sickledex) can screen for HbS, but hemoglobin electrophoresis is the definitive diagnostic test to confirm the presence and quantify HbS.
Common Traps
Warning
While target cells and nucleated red blood cells can be seen in both sickle cell anemia and thalassemia major, the presence of actual sickle-shaped cells is the distinguishing feature that points specifically to sickle cell disease. Do not confuse severe poikilocytosis in thalassemia with true sickling.
Reference
Robbins Basic Pathology, 10th Ed, Ch 13, p. 444-446
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