A patient returning from sub-Saharan Africa presents with fever, anaemia and splenomegaly. Peripheral blood smear shows multiple ring-form trophozoites within a single red cell, some with appliqué (accolé) position, and cytoadherence crescentic gametocytes. Which test would best quantify parasite density and guide severity assessment in this malaria case?
- A Thick blood film with differential count of parasitised erythrocytes per 200 leukocytes ✓
- B Rapid antigen test detecting HRP-2 antigen
- C Thin blood film percentage parasitaemia
- D Quantitative buffy coat (QBC) fluorescent microscopy
Correct answer: A. Thick blood film with differential count of parasitised erythrocytes per 200 leukocytes
Explanation
The thick blood smear is the WHO gold standard for both diagnosis and quantification of malaria parasitaemia; parasite density is calculated per microlitre by counting parasites against 200 leukocytes multiplied by the assumed WBC count (8000/µL). Thin film identifies species by morphology but is less sensitive. HRP-2-based RDTs detect P. falciparum specifically but cannot quantify density or distinguish viable from dead antigen (lag positive after treatment). QBC is sensitive but not recommended for density quantification in routine practice.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.