OnSite (Pf/Pan), a newly available RDT for malaria diagnosis, performed well in this study. OnSite (Pf/Pan) RDT was 96.7% sensitive and 98.6% specific with varying performance for P. falciparum and P. vivax detection. OnSite (Pf/Pan) RDT has inherent capability to detect all types of non-falciparum malaria but only P. vivax was considered in this study due to the absence of Plasmodium malariae and Plasmodium ovale samples in the study areas. In the case of P. falciparum, the sensitivity ranged from 50% to 100% depending on the parasitaemia.
The World Health Organization recommends at least 95% sensitivity of RDTs for low parasite counts
. As like many other malaria RDTs, OnSite (Pf/Pan) failed to achieve this level of sensitivity. However, only six P. falciparum and five P. vivax samples had parasite loads below 100 parasites/μL in this study. Therefore, the low sensitivity observed in low parasitaemia samples may have been driven by the lack of sample size and it cannot be concluded that OnSite (Pf/Pan) does not perform well in low parasitaemia samples.
In the case of P. vivax, the sensitivity consistently increased as the parasite load increased. This supports the idea of the intra-species conserved nature of pLDH
. For P. falciparum, the sensitivity did not always increase as the parasite load increased (Table
3). This occurred because one sample with parasitaemia greater than 1,000 parasites/μL and three samples with parasitaemia greater than 5,000 parasites/μL tested negative by RDT. It is possible that this was caused by deterioration of the target antigen (HRP-2) as the tests were conducted with preserved specimens. Another possibility for this observation is intra-species variation in the gene encoding the HRP gene
 or deletion of the gene
 among different P. falciparum isolates; however this was not assessed, as it was beyond the scope of this study. One negative sample was falsely tested as P. falciparum positive followed by another one as P. vivax by OnSite (Pf/Pan) RDT which might be due to cross reactivity of other infections, such as rheumatoid factor, heteropheline antibodies
. Histidine-rich protein can persist in the blood for more than one month even after a patient is cured of malaria
, which could also be the cause for false positivity in this observation. Conversely, three confirmed P. falciparum samples tested positive in Pan line but HRP2 line did not appear. This might be due to inherent limitation of the device, intra-species variation in the gene encoding the HRP gene or deletion of HRP gene.
OnSite (Pf/Pan) RDT was also incorporated into the WHO RDT evaluation programme in Round 3 and evaluated with good score
. This RDT tested to have 83.8% and 85.7% detection rate/score for P. falciparum and P. vivax, respectively, when parasitaemia were 200 parasites/μL. Furthermore, it had 100% detection rate/score for species in the cases of parasitaemia at 2,000 parasites/μL or more in WHO Panel. This study also reveals an almost similar level of sensitivity especially for higher parasite load, denoting the accuracy of this RDT in identifying symptomatic malaria cases.
OnSite (Pf/Pan) performed better than some similar RDTs developed and widely adopted for malaria diagnosis. Parascreen Pf/Pan RDT was evaluated in different studies
[20–26] where it showed maximum sensitivity of 94% and specificity of 72% for P. falciparum detection. For Pan detection, it showed a maximum sensitivity of 82.5% and specificity of 78.2% for symptomatic patients
OptiMAL (Pf/Pan) is another similar RDT that has been implemented in both the field and the laboratory and has been evaluated several times
[27–30]. Sensitivity ranged from 91.2%-95.4% for P. falciparum and 60.7%-100% for P. vivax malaria while specificity was close to 95% or above
CareStart™ (Pf/Pan) was also evaluated in several experimental conditions
[20, 27, 30–35]. Its overall sensitivity varies from a minimum of 88.24%
 to maximum 95.6%
, while the specificities were close to 95%. The highest sensitivity for P. falciparum diagnosis was observed at 99.4% in Sierra Leone
 while the lowest reported was 85.6% in Ethiopia
 with high specificity in all relevant studies. For P. vivax diagnosis, the highest sensitivity was 92.3% in a study in Madagascar
 while lowest was 85%
 in the same study in Ethiopia where P. falciparum detection sensitivity was lowest
. Specificities of P .vivax detection tests were always very good, above 95% in recent studies.
Compared to the performance of various other RDTs with similar characteristics, OnSite (Pf/Pan) can be considered an effective diagnostic tool for detecting both P. falciparum and P. vivax malaria. This test has high positive predictive value and negative predictive value which indicates that it is capable of detecting true malaria cases as well as excluding non-malaria cases with overlapping symptoms to reduce treatment burden, which happens to be the major concern since artemisinin-based combination therapy is the last oral option presently used in these areas against P. falciparum.
This study used frozen blood samples and well preserved devices for evaluating OnSite (Pf/Pan) RDT, which may not be controlled in field settings. Thus, a slight variant result may be possible in the case of fresh blood samples in ambient field settings.