Rapid diagnosis of vivax malaria by the SD Bioline Malaria Antigen test when thrombocytopenia is present

An easy and reliable diagnostic method for malaria is highly desirable. We examined the recently introduced SD Bioline Malaria Antigen test, which detects Plasmodium lactate dehydrogenase, with the additional aid of the presence or absence of thrombocytopenia to diagnose vivax malaria. We enrolled 732 patients with clinically suspected malaria in an area where vivax malaria is endemic. We performed microscopic examination of thin film, applied the SD Bioline Malaria Antigen test, and checked platelet counts. One hundred ninety-five patients were smear positive for vivax malaria. The sensitivity of the SD Bioline Malaria Antigen test was 96.4%, and its specificity was 98.9%. We found that 95.4% of malaria patients had thrombocytopenia, and the proportion with malaria increased as platelet counts decreased. A positive SD Bioline Malaria Antigen test when thrombocytopenia was present showed a 100% positive predictive value for vivax malaria. In conclusion, the SD Bioline Malaria Antigen test is a rapid and accurate diagnostic method for vivax malaria, and a platelet count can facilitate a rapid diagnosis of malaria.