Which of the following tests would be most useful in confirming the likely diagnosis?
Well done, correct.
Thick and thin blood films are the gold standard for malarial diagnosis however the tests aren't perfect.
They rely heavily on the expertise of the microscopist, and patients with low parasite counts may have negative films at first.
Consequently, if clinical suspicion is high, three films obtained across three consecutive days (one per day) should be obtained before discounting the possibility of malaria. This also allows for identification of parasites across all life cycle stages.