Rapid diagnostic tests (RDTs)
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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 TEST FORMATS and ANTIGENS |
Antigens:
PF specific General PV specific
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 |
The antigens detected by an RDT vary according to the purpose of the test and manufacturers choice. The antigens detected by the tests fall into two groups, but each antigen has strengths and limitations, so it is important to understand which antigens your test uses (see links). 1. “Species-specific antigens”. These detect specific malaria species:
Histidine-rich protein 2 (HRP2): specific for P.falciparum [link] Plasmodium lactate dehydrogenase (pLDH): different forms are specific for either P.falciparum or P.vivax [link]
2. “Pan-malaria antigens”. These detect malaria, but do not indicate the infecting species
a. PpanLDH: a form of LDH present in all malaria species [link]
b. Aldolase: a malaria-specific form of aldolase that is present in all species [link]