Imported malaria with initial negative film — DTM&H MCQ

Correct answer: E — Repeat thick and thin blood films within 12 to 24 hours

The correct answer is E, repeat thick and thin blood films within 12 to 24 hours. A single negative film cannot exclude malaria, particularly with irregular chemoprophylaxis and low, fluctuating parasitaemia early in illness. Current UK laboratory guidance recommends that when clinical suspicion remains high after an initial negative film, repeat films are examined after 12 to 24 hours and again after a further 24 hours, up to a total of three sets. This patient has classic features (fever, headache, myalgia after African travel, thrombocytopenia) that keep falciparum malaria at the top of the differential despite the first negative result, so serial microscopy is mandatory before the diagnosis can be excluded. Why the other options are wrong: D. Perform lumbar puncture before repeat films: there is no meningism or focal neurology described, and malaria must first be excluded with repeat films before invasive tests for alternative diagnoses are pursued. C. Send dengue serology and stop malaria testing: dengue is a reasonable differential in a febrile traveller with thrombocytopenia, but malaria is potentially rapidly fatal and must never be abandoned on the strength of one negative film; serology and film repetition are not mutually exclusive but stopping malaria testing is unsafe. A. Request stool microscopy for ova and parasites: this investigates chronic gastrointestinal parasitic disease, not an acute febrile illness with thrombocytopenia, and has no role in the immediate work-up of suspected malaria. B. Arrange CT abdomen to assess splenomegaly: splenomegaly may support the diagnosis but imaging is not diagnostic for malaria and would delay the definitive test, which is repeat blood film microscopy. Key point: a negative malaria film never excludes malaria; repeat thick and thin films at 12 to 24 hours (up to three sets over 48 hours) is mandatory in a febrile traveller with ongoing suspicion.

Reference: British Society for Haematology, Guidelines for the Laboratory Diagnosis of Malaria (2022), https://onlinelibrary.wiley.com/doi/full/10.1111/bjh.18092