Diagnostic accuracy of a malaria rapid diagnostic test compared with polymerase chain reaction in Lao People’s Democratic Republic: a secondary data analysis

Abstract Background Malaria rapid diagnostic tests (RDTs) are widely used in malaria endemic countries in both clinical and community settings for timely diagnosis, case management and surveillance. Since Greater Mekong Subregion countries approach malaria elimination with residual transmission of low-density Plasmodium spp. infection, the diagnostic accuracy of currently deployed RDTs in Lao People’s Democratic Republic (Lao PDR) was evaluated to inform appropriate deployment of testing strategies in an elimination context. Methods Both residents and mobile migrant populations in five malaria endemic provinces in southern Lao PDR were tested for malaria by village and mobile malaria workers using SD Bioline (now Abbott Bioline™) Malaria Ag P.f/P.v RDT. Archival RDTs were stored and processed for determination of P. falciparum and P. vivax by polymerase chain reaction (PCR), as the reference standard in diagnostic accuracy analyses calculating sensitivity, specificity, positive and negative predictive values, diagnostic odds ratio, positive and negative likelihood ratios and, receiver operating characteristic curve area. Results Among the 10,824 participants, 91 (0.8%) tested positive for malaria by RDT and 193 (1.8%) tested positive by PCR. The overall sensitivity and specificity of the RDT compared to PCR were 36.8% (95% confidence interval (CI): 30.0%–44.0%) and 99.8% (95% CI: 99.7%–99.9%), respectively. Positive and negative predictive values of the RDT were 78.0% (95% CI: 68.1%–86.0%) and 98.9% (95% CI: 98.6%–99.1%), respectively. Parasite species-specific analysis showed that sensitivity for P. falciparum was 73.7% (95% CI: 48.8%–90.9%) and 43.1% (95% CI: 33.4%–53.3%) for P. vivax . Discussion The RDTs evaluated demonstrated low sensitivity in field settings, particularly for P. vivax, when compared with PCR. This most reflects a high proportion of low-density P. falciparum and P. vivax infections that fall below the RDT detection limit, rather than hrp2/3 deletions, which are rare among P. falciparum infections in Lao PDR. Given the predominant prevalence of subclinical low parasite density malaria infection in countries nearing elimination and their potential contribution to ongoing transmission, more sensitive point-of-care diagnostics are needed for surveillance and response activities in elimination settings.