## Diagnosis of Kala-azar: Investigation Hierarchy **Key Point:** Splenic aspiration is the gold standard for diagnosis of kala-azar, with a sensitivity of 95–99%, far superior to bone marrow (75–85%) or peripheral blood smear (<5%). ### Why Splenic Aspiration? 1. **Highest parasite burden**: Amastigotes (Leishman bodies) concentrate in the spleen in kala-azar, making this the optimal tissue for direct visualization. 2. **Procedure**: A fine needle aspiration (FNA) under ultrasound guidance is performed; Giemsa-stained smears reveal oval, intracellular amastigotes within macrophages. 3. **Safety**: Modern ultrasound-guided technique has minimized hemorrhage risk; absolute contraindication only if severe thrombocytopenia (<20,000/μL) or clinical bleeding. ### Comparative Sensitivity of Diagnostic Methods | Investigation | Sensitivity | Specificity | Remarks | |---|---|---|---| | Splenic aspiration + Giemsa | 95–99% | 100% | Gold standard; requires expertise | | Bone marrow aspiration + Giemsa | 75–85% | 100% | Safer; still highly sensitive | | Peripheral blood smear | <5% | 100% | Amastigotes rare in blood | | rK39 serology | 95–98% | 95–98% | Sensitive but cannot distinguish active from past infection | | Blood culture (NNN) | 60–70% | 100% | Slow (2–4 weeks); requires expertise | **High-Yield:** In resource-limited settings where splenic aspiration expertise is unavailable, bone marrow aspiration is an acceptable alternative; serology (rK39) is useful for screening but not confirmatory alone. **Clinical Pearl:** A negative splenic aspiration in a clinically suspicious case is rare; if obtained, repeat aspiration or switch to bone marrow is warranted before excluding kala-azar. **Warning:** ~~Peripheral blood smear~~ is NOT diagnostic for kala-azar — amastigotes are intracellular and sequestered in organs, not circulating freely. [cite:Park 26e Ch 11]
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