Which of the following is the FIRST and most cost-effective investigation in the workup of pancytopenia?

Explanation

## Initial Approach to Pancytopenia Workup **Key Point:** Peripheral blood smear (PBS) examination is the first-line, non-invasive, and cost-effective investigation in any patient with pancytopenia. It provides morphological clues about the underlying etiology before proceeding to invasive procedures. ### Why PBS is First-Line 1. **Non-invasive** — no patient discomfort or procedural risk 2. **Cost-effective** — minimal expense compared to bone marrow procedures 3. **Diagnostic yield** — identifies: - Abnormal cell morphology (blasts, dysplasia, schistocytes) - Hypersegmented neutrophils (B12/folate deficiency) - Spherocytes, polychromasia (hemolysis) - Parasites, inclusions 4. **Guides next step** — findings determine whether bone marrow examination is needed and what type (aspiration vs. biopsy) ### Typical Pancytopenia Workup Algorithm ```mermaid flowchart TD A[Pancytopenia confirmed on CBC]:::outcome --> B[Peripheral Blood Smear]:::action B --> C{Morphology abnormal?}:::decision C -->|Dysplasia/Blasts| D[Bone Marrow Aspiration & Biopsy]:::action C -->|Megaloblastic features| E[B12/Folate levels]:::action C -->|Schistocytes/Spherocytes| F[Hemolysis workup]:::action C -->|Normal morphology| G[Reticulocyte count & Spleen size]:::decision G -->|Low retic, splenomegaly| H[Bone Marrow Exam]:::action G -->|High retic| I[Hemolysis/Immune workup]:::action ``` **High-Yield:** PBS examination is mandatory before bone marrow aspiration in pancytopenia — it is never skipped in standard practice. **Clinical Pearl:** Findings like hypersegmented neutrophils or megaloblastic RBCs on PBS can lead directly to B12/folate measurement, avoiding unnecessary bone marrow procedures.