In the laboratory diagnosis of visceral leishmaniasis (kala-azar), which of the following has the highest sensitivity and is considered the gold standard method?

• A rK39 immunochromatographic test (ICT)
• B Direct agglutination test (DAT)
• C Peripheral blood smear with Giemsa stain
• D Splenic aspirate microscopy for Leishman-Donovan bodies ✓

Explanation

Splenic aspirate microscopy has the highest sensitivity (93–99%) for diagnosing visceral leishmaniasis — amastigotes (Leishman-Donovan or LD bodies) are identified within macrophages. However, due to risk of fatal haemorrhage, it is only performed when prothrombin time and platelet count are adequate and coagulation is normal. The rK39 ICT is highly sensitive (>90%) and specific and is widely used as a point-of-care test; it is the preferred field test in India's national elimination programme. Peripheral blood smear is less sensitive (~50–70%) and is more useful in immunocompromised hosts or HIV co-infection where parasitaemia is high.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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