Rapid diagnostic tests (RDTs): Difference between revisions
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<span style="font-size:90%">It is essential to appreciate that RDT tests provide a rapid means to indicate the presence of malaria infection. They are rapid and in some cases th only choice, but should never be considered to be a fully reliable or "gold standard" test. These problems are discussed in later sections but briefly: | <span style="font-size:90%">It is essential to appreciate that RDT tests provide a rapid means to indicate the presence of malaria infection. They are rapid and in some cases th only choice, but should never be considered to be a fully reliable or "gold standard" test. These problems are discussed in later sections but briefly: | ||
*<span style="font-size:90%">Tests made vary in quality or sensitivity, either manufacturer or | *<span style="font-size:90%">Tests made vary in quality or sensitivity, either by manufacturer or due to batch variation. The World Health Organisation has a rolling programme that evaluates performance of different tests. | ||
*<span style="font-size:90%">Practical aspects of use are vital: tests must be stored, performed and read correctly - this is one of the mast important causes of test failure world-wide. | *<span style="font-size:90%">Practical aspects of use are vital: tests must be stored, performed and read correctly - this is one of the mast important causes of test failure world-wide. | ||
*<span style="font-size:90%">Sensitivity and false positive rates vary between species, and also according to the detection system used. Most tests have a significantly reduced sensitivity at lower parasite concentrations. You should be aware of the strengths and limitations of the test you use. | *<span style="font-size:90%">Sensitivity and false positive rates vary between species, and also according to the detection system used. Most tests have a significantly reduced sensitivity at lower parasite concentrations. You should be aware of the strengths and limitations of the test you use. | ||
Sensitivities are broadly summarised below: | Sensitivities are broadly summarised below: | ||
(Table) | |||
Revision as of 11:24, 26 July 2024
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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 BASICS |
It is essential to appreciate that RDT tests provide a rapid means to indicate the presence of malaria infection. They are rapid and in some cases th only choice, but should never be considered to be a fully reliable or "gold standard" test. These problems are discussed in later sections but briefly:
- Tests made vary in quality or sensitivity, either by manufacturer or due to batch variation. The World Health Organisation has a rolling programme that evaluates performance of different tests.
- Practical aspects of use are vital: tests must be stored, performed and read correctly - this is one of the mast important causes of test failure world-wide.
- Sensitivity and false positive rates vary between species, and also according to the detection system used. Most tests have a significantly reduced sensitivity at lower parasite concentrations. You should be aware of the strengths and limitations of the test you use.
Sensitivities are broadly summarised below:
(Table)
| 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 |