Rapid diagnostic tests (RDTs): Difference between revisions
From MalariaETC
No edit summary |
No edit summary |
||
| Line 26: | Line 26: | ||
<span style="font-size:90%">It is essential to appreciate that RDT tests meet a specific task:</br> | <span style="font-size:90%">It is essential to appreciate that RDT tests meet a specific task:</br> | ||
''' | '''RDTs provide a rapid means to indicate the possible presence or absence of malaria infection''' | ||
While in some circumstances they are the only choice, RDTs should never be considered to a "gold standard" test, and the significant issues with particular speces and with low parasite counts must be recognised. Briefly: | While in some circumstances they are the only choice, RDTs should never be considered to a "gold standard" test, and the significant issues with particular speces and with low parasite counts must be recognised. Briefly: | ||
| Line 36: | Line 36: | ||
Sensitivities are broadly summarised below: | Sensitivities are broadly summarised below: | ||
( | <div style="width: 95%; font-size:90%;"> | ||
{| class="wikitable" style="border-style: solid; border-width: 4px; color:black" | |||
!colspan="1" style = "background:#ddeee1; border:solid; border-width: 3px;"|<span style="font-size:90%;">'''Demonstrating primitive phenotype in AML'''</span></br> | |||
|- | |||
!colspan="1" style = "background:white; border:solid; border-width: 1px; color:black"|In most cases, cells of AML will demonstrate typical features of immature cells with: '''weak expression of CD45''', and expression of '''CD34''' and/or '''CD117'''</br>However, patterns are not always typical and difficult cases other markers of early differentiation may also help</br></br>[[Markers used to demonstrate primitive nature in AML|''Click for a more detailed table of markers associated with primitive phenotype'']] | |||
|- | |||
!colspan="1" style = "background:#ddeee1;border:solid"|<span style="font-size:90%;">'''Difficulties may occur where blast cells have significant maturation so their primitive nature may be less easy to demonstrate.'''</span></br> | |||
|- | |||
!colspan="1" style = "background:white; border:solid; border-width: 1px;"|Difficulties are most frequently encountered in monocytic cases of AML, or in acute promyelocytic leukaemia (APL) (although occasionally in other types).</br></br>[[Atypical patterns of primitive marker expression in acute myeloid leukaemia|Click to see common patterns that may cause difficulty in assigning primitive phenotype]] | |||
|- | |||
|} | |||
</div> | |||
Revision as of 11:48, 29 July 2024
Navigation
Return to Main index
| 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 meet a specific task:
RDTs provide a rapid means to indicate the possible presence or absence of malaria infection
While in some circumstances they are the only choice, RDTs should never be considered to a "gold standard" test, and the significant issues with particular speces and with low parasite counts must be recognised. 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:
| Demonstrating primitive phenotype in AML |
|---|
| In most cases, cells of AML will demonstrate typical features of immature cells with: weak expression of CD45, and expression of CD34 and/or CD117 However, patterns are not always typical and difficult cases other markers of early differentiation may also help Click for a more detailed table of markers associated with primitive phenotype |
| Difficulties may occur where blast cells have significant maturation so their primitive nature may be less easy to demonstrate. |
| Difficulties are most frequently encountered in monocytic cases of AML, or in acute promyelocytic leukaemia (APL) (although occasionally in other types). Click to see common patterns that may cause difficulty in assigning primitive phenotype |
| 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 |