The peripheral blood smear shown above demonstrates a leukocyte with a bilobed nucleus and abundant coarse, bright red-orange cytoplasmic granules. This cell is most accurately identified as a/an:

Explanation

## Image Findings * A large leukocyte is visible amidst numerous red blood cells. * The nucleus is distinctly **bilobed** and stained dark blue/purple. * The cytoplasm is filled with numerous, relatively **large, coarse, bright red-orange (eosinophilic) granules**. * The cell size appears larger than surrounding red blood cells. ## Diagnosis **Key Point:** The cell shown is an **Eosinophil**, characterized by its bilobed nucleus and prominent, coarse, bright red-orange cytoplasmic granules. Eosinophils are granulocytes that constitute 1-6% of the total white blood cell count. Their most distinctive feature under light microscopy, especially with Romanowsky stains (like Leishman or Giemsa), is the presence of large, acidophilic (eosinophilic) granules that stain bright red-orange. The nucleus is typically bilobed or occasionally trilobed, but rarely multilobed like a neutrophil. ## Differential Diagnosis | Feature | Eosinophil | Neutrophil | Basophil | Monocyte | | :---------------- | :------------------------------------------ | :------------------------------------------ | :------------------------------------------ | :-------------------------------------------- | | **Nucleus** | Bilobed (often spectacle-shaped) | 3-5 lobes (multilobed) | Irregular, often bilobed, frequently obscured | Kidney-shaped, horseshoe-shaped, or convoluted | | **Cytoplasmic Granules** | Coarse, large, bright red-orange (eosinophilic) | Fine, small, pink/lilac (neutral) | Coarse, large, dark blue/purple (basophilic), often obscure nucleus | Absent or very fine, dust-like azurophilic granules | | **Cytoplasm Color** | Pale pink/clear, filled with granules | Pale pink | Pale pink/clear, filled with granules | Abundant, gray-blue, often vacuolated | ## Clinical Relevance **Clinical Pearl:** Eosinophilia (increased eosinophil count) is commonly associated with **allergic reactions** (e.g., asthma, hay fever, drug reactions), **parasitic infections** (especially helminthic infections), and certain **skin diseases** (e.g., eczema, pemphigus). Less commonly, it can be seen in some malignancies (e.g., Hodgkin lymphoma) and autoimmune conditions. ## High-Yield for NEET PG **High-Yield:** Eosinophil granules contain major basic protein, eosinophil cationic protein, eosinophil-derived neurotoxin, and eosinophil peroxidase, which are cytotoxic to parasites and host tissues. **Key Point:** Eosinophils play a crucial role in the immune response against parasites and in the pathogenesis of allergic diseases. ## Common Traps **Warning:** Distinguishing eosinophils from basophils is important. While both have coarse granules and can have bilobed nuclei, basophil granules are dark blue/purple and often obscure the nucleus, whereas eosinophil granules are distinctly red-orange and the bilobed nucleus is usually clearly visible. ## Reference [cite:Robbins Basic Pathology, 10th Edition, Chapter 13: Hematopoietic and Lymphoid Systems]