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ANNEX 5. Malaria diagnosis

dehydrogenase (pLDH) or pan-specific aldolase. These antigens have different
characteristics, which may affect suitability for use in different situations, and these
should be taken into account when developing RDT policy. These tests have many
potential advantages, including:
• the ability to provide rapid results;
• fewer requirements for training and skilled personnel (for instance, a general health
worker can be trained in one day);
• reinforcement of patient confidence in the diagnosis and in the health service in general.

There are also potential disadvantages, including:
• the likelihood of misinterpreting a positive result as indicating malaria in patients with
parasitaemia incidental to another illness, in particular when host immunity is high;

• the inability, in the case of some RDTs, to distinguish new infections from a recently
and effectively treated infection; this is due to the persistence of certain target antigens
(e.g. HRP2) in the blood for 1–3 weeks after effective treatment;
• unpredictable sensitivity in the field (13–20); this can be reduced by careful procurement,
testing, and good transport and storage. WHO facilitates lot (batch) testing prior to A5
field deployment.

Published sensitivities of RDTs for P. falciparum range from comparable to those of
good field microscopy (> 90% at 100–500 parasites/μl of blood) to very poor (40–50%)
for some widely used products. Sensitivities are generally lower for other species. The
reasons for poor sensitivity may include: poor test manufacture; damage due to exposure
to high temperature or humidity; incorrect preparation and interpretation by end-users;
and variation in the target antigen (12). Several studies have shown that health workers,
volunteers and private sector providers can, with adequate training and supervision, use
RDTs correctly and provide accurate malaria diagnosis.
The use of a confirmatory diagnosis with either microscopy or RDTs is expected to
reduce the overuse of antimalarials by ensuring that treatment is targeted at patients
with confirmed malaria infection, as opposed to treating all patients with fever. However,
although providers of care may be willing to perform diagnostic tests, they do not always
comply with the results. This is especially true when they are negative. It is, therefore,
important to ensure the accuracy of parasite-based diagnosis and demonstrate this to
end-users, and to provide them with the resources to adequately manage both positive
and negative results.

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