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Rapid diagnostic tests (RDTs)

From MalariaETC


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OVERVIEW

RDTs detect malarial parasite antigens in the blood of infected individuals. Precise test formats can differ according to manufacturer and purpose, but follow similar principles using either a plastic cassette or a folding card. The simplest format (with a single test and control line) is shown below.

Essentially, a lysis buffer will be introduced to the test through one window and a sample of blood is introduced into the second window. The interaction between buffer and sample will breakdown the red cells and any malaria parasites; this lysed sample they will diffuse along the strip where labelled antibodies will be used to detect the presence of parasites, forming a visible band in one or more test windows (T). Successful test performance will be shown by the appearance of a control band (C).



THE ANTIGENS


Different antigens offer different benefits or drawbacks. The antigens used in your test should be considered when interpreting results:


Species-specific antigens that detect individual malaria species:

  • Histidine-rich protein 2 (HRP2): specific for P.falciparum - Click for details
  • Plasmodium falciparum lactate dehydrogenase (PfLDH): specific for P.falciparum - Click for details
  • Plasmodium lactate dehydrogenase (PVLDH): specific for P.vivax - Click for details


Pan-specific antigens that detect the presence of any malaria species:

  • Plasmodium lactate dehydrogenase (PLDH): a form of LDH that is present in all malaria species Click for details
  • Pan-Plasmodium Aldolase Antigen (Aldolase): a malaria-specific form of aldolase that is present in all species Click for details


TEST FORMATS

The following formats are available:

Single band tests (comprising a single test band and a control) (image)

  • simplicity and lower cost
  • suitable only where there is a sigle dominant malaria species.

The single secies P.falciparum diagnostic test has been successfully applied in Africa areas where infections with this species account for more than 95% of infections.

Multi-band tests: the most frequent form identifies the dominant or most important species with a species-specific band for the selected region, then a second band idetifies antigens expressed by all malaria species. Two formats are used:

PF/general PV/general

Test selection


INTERPRETATION and PROBLEMS