How do RDT tests compare to microscopy?

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RDT Tests compared with microscopy

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The value of RDT tests compared with microscopy: thick blood films It is important in all cases however to understand the limitations of the test used (microscopy or RDT) in terms of species identiication and sensitivity. 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 where equipment, staining quality, or microscopic experience is less good, then RDTs may have equivalent or superior sensitivity to microscopy. This includes many malarial endemic regions where microscopy may be unavailable or where the sensitivity of microscopy is limited by training, equipment or facilities. The value of RDT tests compared with microscopy: thin blood films Thin films may provide similar sensitivity for diagnosis to thick films to a routine laboratory where an experienced morphologist has sufficient time and experience and is able to follow recommended practices by examining a large number of microscopic fields. The thin-film format may be preferred by users are less familiar with thick films and feel more comfortable with thin film appearances. However, this is not the currently recommended practice for diagnosis. Thin films do however offer particular advantages for the assessment of cases once a diagnosis of malaria has ben made: (1) For species identification thin films are preferred to thick films or RTDS (including mixed infections) as they allow accurate assesment of sepcies specific features Where cases require the % of infected red-cells to be determined (P.falciparum or P.knowlesi) this is much more accurately assessed by thin film. Under what circumstances may a RDT be preferred? (1) RDT tests are less affected by operator skill, facilities or training. They may provide a diagnostic sensitivity that is as good or better than morphology where expertise is limited, and may be the only choice where conditions do not allow microscopy. (2) RDTs provide a more rapid turnaround time allowing emergency use and rapid decision-making. (3) When used together with morphology RDTs may help increase diagnostic confidence compared with when either is used alone. (4) The use of RDTs may provide an overall cheaper diagnostic alternative in low-income countries.