The utility of serial blood film testing for the diagnosis of malaria.

Current guidelines on the diagnosis and exclusion of malaria stipulate that if there is an initial negative result on blood film, multiple blood film preparations should be taken to sufficiently exclude malaria.We looked at a state-wide database of blood results retrospectively for a period of 14 years to identify subjects who had been tested for malaria.Most (93%) of patients were diagnosed on the first blood smear. Almost 7% of patients had an initial negative blood film result but subsequently went on to have a positive result. The majority of patients diagnosed with malaria on the first blood film had Plasmodium falciparum (66%) whilst the majority of patients with an initial negative blood film result were later diagnosed with P. vivax (78%).Most of the subjects in the 7% group were members of the Australian Defence Force and would have received chemoprophylaxis against malaria.The majority of malaria diagnoses are confirmed on a single blood film result. However, a significant proportion of malaria diagnoses would be missed if only one blood film were examined. Currently there is insufficient clinical and epidemiological information to predict which subjects would require one versus three blood film examinations. As such, three blood films should be obtained for patients suspected of having malaria.