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?

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. ## Differential Diagnosis | Feature | Sickle Cell Anemia | Iron Deficiency Anemia | Hereditary Spherocytosis | Thalassemia Major | | :------------------ | :----------------------------------------------- | :------------------------------------------------------ | :------------------------------------------------------- | :------------------------------------------------------ | | **Key RBC Morphology** | **Sickle cells**, target cells, NRBCs, Howell-Jolly bodies | Microcytic, hypochromic, pencil cells, anisopoikilocytosis | **Spherocytes**, increased MCHC, reticulocytosis | Microcytic, hypochromic, target cells, tear drop cells, **numerous NRBCs** | | Hemoglobin | HbS | Decreased Hb, MCV, MCH | Normal Hb, MCV, MCH (unless severe anemia) | Decreased Hb, MCV, MCH, increased HbF | | Pathophysiology | HbS polymerization, chronic hemolysis, vaso-occlusion | Impaired heme synthesis | Defective spectrin/ankyrin, membrane instability, extravascular hemolysis | Reduced/absent globin chain synthesis, ineffective erythropoiesis | ## Clinical Relevance **Clinical Pearl:** 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). ## High-Yield for NEET PG **High-Yield:** 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 [cite:Robbins Basic Pathology, 10th Ed, Ch 13, p. 444-446]