A 32-year-old man from Bihar presents with a 3-month history of fever, weight loss, and hepatosplenomegaly. Peripheral blood smear shows no parasites. Which investigation is most appropriate to confirm the diagnosis of visceral leishmaniasis (kala-azar)?

Explanation

## Diagnosis of Visceral Leishmaniasis **Key Point:** Bone marrow aspiration is the gold standard investigation for confirming kala-azar when peripheral blood smear is negative. ### Why Bone Marrow Aspiration? In visceral leishmaniasis, *Leishmania donovani* amastigotes preferentially localize to **reticuloendothelial tissue** (bone marrow, spleen, liver). The parasite burden in bone marrow is 100–1000 times higher than in peripheral blood, making aspiration the most sensitive diagnostic method. **High-Yield:** Amastigotes appear as **oval, intracellular bodies** (2–3 μm) within macrophages and monocytes on Giemsa staining. They contain a characteristic **kinetoplast** (rod-shaped DNA organelle). ### Diagnostic Yield by Site | Site | Sensitivity | Notes | | --- | --- | --- | | **Bone marrow** | 90–95% | Gold standard; most practical | | Spleen | 95–98% | Higher yield but invasive; risk of rupture | | Liver | 80–85% | Lower yield than marrow | | Peripheral blood | <10% | Rarely positive except in immunocompromised | **Clinical Pearl:** In endemic areas (Bihar, Jharkhand, West Bengal), bone marrow aspiration from the anterior iliac crest or sternum is the preferred first-line confirmatory test because it is safe, accessible, and highly sensitive. ### Comparison with Other Investigations ```mermaid flowchart TD A[Suspected Kala-azar]:::outcome --> B{Clinical + epidemiologic clues present?}:::decision B -->|Yes| C[Bone marrow aspiration + Giemsa]:::action C --> D[Amastigotes visualized?]:::decision D -->|Yes| E[Diagnosis confirmed]:::outcome D -->|No| F[rK39 serology or PCR]:::action B -->|No| G[Serology first]:::action ``` **Mnemonic:** **BMAS** = **B**one marrow **A**spiration is **S**tandard for kala-azar diagnosis. [cite:Park 26e Ch 8]