Antigen capture immuno-chromatographic strip format in detecting parasite-specific lactate dehydrogenase to diagnose malaria in nonimmune patients

Abstract

Several rapid diagnostic test devices (RDT) based on detection of malaria antigen in the whole blood were developed. OptiMal test the presence of parasite-specific lactate dehydrogenase (LDH) enzyme using three monoclonal antibodies was used. Two monoclonal antibodies were pan-specific and recognized all malaria species. The third one was specific only for Plasmodium falciparum. The parasite antigens were detected using an antigen-capture immunochromatographic strip format. One hundred-nine malaria positive and 730 malaria negative cases diagnosed by microscopy were included. 75/109 were P. falciparum 26 as P. vivax, 3 P. malariae and 5 mixed infection of P. falciparum & P. vivax. The RDT showed a low sensitivity (85%, 95% Confidence Interval [CI], 79-92%) with a much lower sensitivity in detecting species other than P. falciparum as well as in mixed infections. The sensitivity was 50% for less than 200 parasites/micro. The sensitivity of OptiMal for P. falciparum was 87% (95% CI, 79-94), 81% (95% CI, 66-96) for P. vivax, and failed with P. malariae. Mixed infections were misdiagnosed as Pfalciparum. The sensitivity of OptiMal was quite good in detecting both P. falciparum & P. vivax (98%; 95% CI, 97-99 & 100%; 95% CI, 100-100 respectively) and 99% (95% CI, 98-99) for all species. The positive and negative ratio for all malaria species was: (+LR = 62.3, -LR = 0.01); for P. falciparum (+LR = 38.9, -LR = 0.01) and for P. vivax (+LR = 0.8077/0, -LR = 0.2). The test value to assess drug resistance in post treatment days was discussed.