Malaria rapid diagnostic test interpretation — DTM&H MCQ

Correct answer: A — Urgent malaria microscopy with speciation and parasite count

The correct answer is A, urgent malaria microscopy with speciation and parasite count. A positive HRP2-based rapid diagnostic test only signals falciparum antigen and cannot speciate mixed or non-falciparum infection, cannot quantify parasitaemia, and can remain positive for weeks after successful treatment due to persistent antigenaemia. UK guidance is explicit that RDTs are a supplement, not a replacement, for expert microscopy, since thick and thin films remain the reference standard for detecting and speciating parasites and for calculating percentage parasitaemia, which drives decisions on severity and need for artesunate versus oral therapy. Because this patient is stable but has a positive RDT and delayed microscopy, urgent expert film examination is required before any species-specific or severity-based treatment decision can be made safely. Why the other options are wrong: C. Lumbar puncture: there is no meningism or focal neurology described, and cerebral malaria or bacterial meningitis is not suggested by the stem, so this invasive test is unjustified before basic diagnostic confirmation. D. Chest radiograph: no respiratory symptoms, hypoxia, or signs of ARDS are described, so imaging the chest does not address the diagnostic priority here. E. Empirical praziquantel: this treats schistosomiasis or other trematode infection, which is clinically unrelated to a positive malaria antigen test, and treating blind without speciation risks masking or delaying appropriate antimalarial therapy. B. Dengue IgG serology: IgG indicates past rather than acute infection and does not help when a malaria RDT is already positive; it does not address the urgent need to confirm species and parasite burden. Key point: A positive malaria RDT must always be confirmed and quantified by urgent expert microscopy because antigen tests cannot reliably speciate or measure parasitaemia, both of which determine treatment.

Reference: UK malaria treatment guidelines 2016, Journal of Infection (PHE/UK guideline group), Diagnosis section: microscopy of thick and thin films by an expert is the optimum diagnostic procedure for detection and speciation of malaria, with RDTs as a supplement rather than a replacement, https://www.journalofinfection.com/article/S0163-4453(16)00047-5/fulltext