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Methodology for malaria testing
Medical expert of the article
Last reviewed: 06.07.2025
Parasitological diagnostics of malaria is based on the detection of asexual and sexual forms of the pathogen during microscopic examination of blood, which is possible only during its development in the erythrocyte. To detect plasmodia and determine their type, blood preparations prepared by the "thin smear" and "thick drop" methods, stained according to Romanovsky-Giemsa, are used. Both methods, which have their advantages and disadvantages, are complementary.
Detection of any stages of plasmodia (even 1 parasite) developing in erythrocytes (trophozoites - young and adult, schizonts - immature and mature, as well as sexual forms of gametocytes - male and female) in a blood smear or thick drop is the only indisputable proof of malaria. It should be borne in mind that the volume of blood examined in a thick drop is 20-40 times greater than in a thin smear, therefore a positive answer can be given even after examining a smear, and a negative one - only after examining a thick drop with an immersion lens for at least 5 minutes, with viewing at least 100 fields of view (WHO standard).
The sensitivity of the thick film method is such that approximately 8 parasites can be detected in 1 µl of blood when examining 100-150 fields of view. Caution should be exercised when detecting a single formation resembling a ring-shaped trophozoite in a thick film, since the appearance of this stage of the parasite can be simulated by various artifacts. If, in case of suspected malaria, plasmodia cannot be detected in a single blood test, it is sometimes necessary to conduct multiple tests (in tropical malaria, blood smears should be taken every 6 hours throughout the attack).
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