Malaria Rapid Test (MRDT)

Description

Malaria rapid diagnostic tests (RDTs) assist in the diagnosis of malaria by providing evidence of the presence of malaria parasites in human blood. RDTs are an alternative to diagnosis based on clinical grounds or microscopy, particularly where good quality microscopy services cannot be readily provided.

Mode of action of common malaria RDT format

1. The first step of the test procedure involves mixing the patient’s blood with a lysing agent in a test strip or well. This ruptures the red blood cells, releasing more parasite protein.

2. Dye-labelled antibody, specific for target antigen, is present on the lower end of nitrocellulose strip or in a plastic well provided with the strip. Antibody, also specific for the target antigen, is bound to the strip in a thin (test) line, and either antibody specific for the labelled antibody, or antigen, is bound at the control line.

3. Blood and buffer, which have been placed on strip or in the well, are mixed with labelled antibody and are drawn up the strip across the lines of bound antibody.

4. If antigen is present, some labelled antibody-antigen complex will be trapped and accumulate on the test line. Excess-labelled antibody is trapped and accumulates on the control line. A visible control line indicates that labelled antibody has traversed the full length of the strip, past the test line, and that at least some free antibody remains conjugated to the dye and that some of the capturing properties of the antibodies remain intact.

5. The intensity of the test band will vary with the amount of antigen present, at least at low parasite densities (antigen concentration), as this will determine the amount of dye particles which will accumulate on the line. The control band intensity may decrease at higher parasite densities, as much of the labelled antibody will have been captured by the test band before reaching the control.