Microscopy and RDT test sensitivity

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The value of RDT compared with microscopy: thick blood films In ideal conditions: A well-trained microscopist with experience in malaria, viewing a well-prepared thick blood film using a good quality microscope may detect better than 1 infected cell per 1000 total red cells. This is equivalent to around 50 parasites/ul. However, in practice it is estimated that a less experienced microscopist in equivalent conditions may acheive less sensitivity - perhaps 1 parasite in 100 red cells - equivalent to 500 parasites/μl. Both these outcomes are as good or better than an RDT test for detecting P.falciparum, and exceed what might be expected for other malaria species. In less ideal conditions: If equipment, staining quality, or microscopic experience is less good, then RDTs may have equivalent or superior sensitivity to microscopy. However, it is important in these conditions to understand the limitations of the selected test in terms of species identiication and sensitivity.

The value of RDT compared with microscopy: thick blood films Compare with RDTs: P.falciparum is identified in the range x-y. Non-falciparum species are identified in the range x-y Other advantages: thin: may provide similar sensitivity to a routine lab if sufficient cells are examined but this is time consuming. Thin films identify all species and allow species recognition including mixed infection and are unaffected by problems of gene deletion or poorly-detected species. Allow parasite level to be detected. Achievable sensitivity: these outcomes are highly dependent on the quality of preparation, the facilities available to examine the film, and the skill of the operator. In many malarial endemic regions this sensitivity will not be achieved. RDTs Less affected by operator skill, facilities or training: may be at least as good as morphology where expertise is limited. Provide a more rapid turnaround time. Disadvantages compared with blood: False negatives and poor at some species Conclusions