Use of latex microbeads for detection of Plasmodium vivax lactate dehydrogenase using flow cytometry.

Malaria is a parasitic disease of great relevance in global public health. The development of new sensitive and specific diagnostic high-throughput methods remains a challenge in the eradication of this disease. In this study, we developed a flow cytometry test using latex microbeads and polyclonal antibodies obtained from rabbits and mice for the detection of the P. vivax lactate dehydrogenase (PvLDH) antigen. We processed 50 samples from Brazilian patients diagnosed with malaria caused by P. vivax and 40 samples from healthy individuals. The assay presented sensitivity of 64%, specificity of 97%, a positive predictive value of 97%, and a negative predictive value of 57% when analyzed using the fluorescent labeling method. Using the mean fluorescence intensity (MFI) analysis method, the sensitivity was 53%, specificity was 89%, the positive predictive value was 95%, and the negative predictive value was 33%. In both methods of analysis, we observed significant statistical differences between the analyzed groups (P-value <0.0001). A high correlation (0.60) between the two methods and a low correlation between PvLDH concentration and parasite density was found. The test was able to detect the PvLDH protein with high specificity, but its sensitivity should be improved. More promising results were observed when the samples were analyzed according to the percentage of fluorescent labeling. Improvement of this assay would enable its application as a serological test for the detection of asymptomatic patients and for the validation of rapid diagnostic tests.