The role of RDTs in malaria control

Malaria rapid diagnostic tests (RDTs) can assist in making a rapid, accurate diagnosis of malaria in circumstances where microscopy-based diagnosis may be not available or unreliable.

To enable effective diagnosis of all malaria cases, the diagnostic method used must be accurate and available at the point of care.

RDTs may be useful in:

• diagnosis by health workers distant from good microscopy services;
• remote diagnosis in organized workforces entering malaria-endemic areas (i.e. military or mining companies); and
• outbreak investigation and surveys of parasite prevalence.

RDTs can offer significant benefits in malaria management if:

• a clear plan of action has been prepared to deal with the outcomes (i.e. drug treatment or appropriate further investigation);
• a clear benefit is demonstrated in health outcomes;
• they are affordable; and
• there are adequate systems in place to ensure RDTs are used correctly and are in good condition.

Use of malaria RDTs in clinical management

The following issues are important for successful incorporation of RDTs into malaria control:

• Clear benefit is obtained by parasitological confirmation of malaria diagnosis.
• Accuracy of RDTs can be regularly monitored (quality control).
• A "cool chain" is in place for transport and storage.
• Good health worker training, supervision and monitoring is in place.
• A clear policy of action on results is in place.

These elements must be allowed for in the RDT budget.

Accuracy of results

RDTs should be sensitive enough to reliably detect malaria parasites at densities associated with disease. Sensitivity is determined by the quality of manufacture, species, number, viability and strain of parasites present, condition of the RDT (including storage conditions), technique and care used in performing the test as well as reader’s interpretation.

Sensitivity will always depend on the concentration of target antigen (protein) present and will therefore vary with parasite density. The same test may achieve a high sensitivity in a population in which all infected people have a high parasite density (e.g. above 10 000 parasites/µl), but achieve low sensitivity in areas where parasite densities are frequently below 200 parasites/µl; therefore, sensitivity stated by manufactures based on field trials can only be integrated if the parasite density of the study population is known.

Ultimately, it is important that both sensitivity and specificity remain high, so that both malaria and non-malarial fevers receive appropriate management. However sometimes it may be more important to have very high sensitivity even at the expense of high specificity, as a missed parasitaemia may lead to death of a patient.