RDT for mallaria

The RDT works through the lateral flow or Immunochromatographic Strip method and signifies the presence of antigens by a colour change/formation of bands on an absorbing nitrocellulose strip.

The RDTs come in a number of formats:

• Card
• Dipstick
• Hybrid cassette-dipsticks
• Plastic cassette

The three main groups of antigens detected by commercially available RDTs are:

1. Histidine-rich protein 2 (HRP-2), specific to P. falciparum. It is an abundant soluble, heat stable
   antigen that is present in the cytoplasm and membrane of infected erytocytes.
2. Parasite specific plasmodium lactate dehydrogenase (pLDH), currently available as P. falciparum specific,
   pan-specific, and P. vivax-specific pLDH antibodies.
3. Aldolase (pan-specific). These two antigens are conserved major enzymes in the glycolytic pathway
   of malaria parasites, they are abundant and are soluble in the parasite.

Target antigens for commercially available RDTs:

Antigens Species	HRP2	PLDH	Aldolase
P. falciparum specific	√	√
Pan-specific (all species)		√	√
P. vivax specific		√

Note: Pan-specific means that the RDT detects all the four types of plasmodia that infect humans.

Technique: A blood specimen collected from the patient is applied to the sample pad on the test card along with certain reagents. After 15 mins, the presence of specific band in the test card window indicate whether the patient is infected with Plasmodium falciparum or one of the other three species of human malaria.

Advantage of Rapid Diagnostic test for Malaria diagnosis)
High quality malaria microscopy is not always available in every clinical settings where patients might seek medical attention. The laboratories associated with these health care settings may now use an RDT to more rapidly determine if their patients are infected with malaria.

1. Relatively easy to use with minimal training required
2. Relatively rapid, giving timely results
3. Little or no manipulation of sample required, can be performed in places without laboratories
4. Most of the RDTs do not require refrigeration, hence tests can be performed where there is no power supply
5. Uses whole blood (prick or venous blood prick preferred) 

Disadvantage of Rapid Diagnostic test (for Malaria diagnosis)

1. Costs per test may exceed those of microscopy.
2. Short shelf-life, requiring efficient procurement, transportation, storage and distribution systems
3. Most tests are qualitative (i.e. gives a yes or no answer). Any quantification of parasitemia will require further
   laboratory-based tests
4. Intensity of test band varies with amount of antigen present at low parasite densities-this may lead to
   reader variation in test results
5. In many cases, they are less sensitive (and less specific) than laboratory based tests. The RDT may not be able to detect some infections with lower number of malaria parasites circulating in the patient’s bloodstream.
6. The use of the RDT does not eliminate the need for malaria microscopy. All negative RDT must be followed by microscopy to confirm the result.In addition, all positive RDT’s should also followed by microscopy.