Which of the following is the FIRST-LINE investigation in the diagnostic workup of pancytopenia?

Explanation

## First-Line Investigation in Pancytopenia Workup **Key Point:** Peripheral blood smear examination is the initial and most cost-effective screening investigation in any patient presenting with pancytopenia. ### Why Peripheral Blood Smear? The peripheral smear provides critical morphological information that guides all subsequent investigations: - **Cell morphology:** Identifies dysplastic changes, abnormal blasts, immature cells - **RBC abnormalities:** Schistocytes, spherocytes, hypersegmented neutrophils - **Platelet assessment:** Size, granularity, clumping - **WBC differential:** Presence of atypical lymphocytes, blast cells, toxic granulations ### Diagnostic Algorithm ```mermaid flowchart TD A[Pancytopenia suspected]:::outcome --> B[Peripheral blood smear]:::action B --> C{Morphology findings?}:::decision C -->|Dysplasia/Blasts| D[Bone marrow biopsy]:::action C -->|Normal morphology| E[Assess reticulocyte count]:::action E -->|Low| F[Hypoplasia suspected]:::outcome E -->|Normal/High| G[Peripheral destruction]:::outcome F --> H[Bone marrow biopsy]:::action G --> I[Specific tests: DAT, LDH, bilirubin]:::action ``` ### Role of Other Investigations | Investigation | Timing | Indication | |---|---|---| | **Peripheral smear** | **First** | All cases | | **Bone marrow biopsy** | Second | Suspected hypoplasia, dysplasia, or malignancy | | **Flow cytometry** | Selective | Suspected hematologic malignancy or immune cytopenias | | **Cytochemical stains** | Selective | Classification of AML or lymphoid neoplasms | **High-Yield:** The smear takes 5 minutes, costs ₹50–100, and eliminates 70% of diagnostic possibilities before ordering expensive tests like bone marrow biopsy (₹3,000–5,000) or flow cytometry (₹5,000–8,000). **Clinical Pearl:** A hypersegmented neutrophil (>5 lobes) on smear immediately suggests vitamin B₁₂ or folate deficiency, directing you toward serum B₁₂, folate, and methylmalonic acid levels rather than bone marrow sampling.