Diagnosis of malaria

Diagnosis

Malaria should be considered in the differential diagnosis of anyone who presents with a febrile illness in, or having recently left, a malarious area. Falciparum malaria is unlikely to present more than 3 months after exposure, even if the patient has been taking prophylaxis, but vivax malaria may cause symptoms for the first time up to a year after leaving a malarious area.
Diagnosis is usually made by identifying parasites on a Giemsa-stained thick or thin blood film (thick films are more difficult to interpret, and it may be difficult to speciate the parasite, but they have a higher yield). At least three films should be examined before malaria is declared unlikely. An alternative microscopic method is quantitative buffy coat analysis (QBC), in which the centrifuged buffy coat is stained with a fluorochrome which 'lights up' malarial parasites. A number of antigen-detection methods for identifying malarial proteins and enzymes have been developed. Some of these are available in card or dipstick form, and are potentially suitable for use in resource-poor settings. Serological tests are of no diagnostic value.
Parasitaemia is common in endemic areas, and the presence of parasites does not necessarily mean that malaria is the cause of the patient's symptoms. Further investigation, including a lumbar puncture, may be needed to exclude bacterial infection.