Malaria rapid diagnostic tests: Plasmodium falciparum infections with high parasite densities may generate false positive Plasmodium vivax pLDH lines

Nine P. vivax-specific RDTs were tested with 85 P. falciparum samples of high (≥2%) parasite density. Mixed P. falciparum/P. vivax infections were ruled out by real-time PCR. The RDTs included two-band (detecting Pv-pLDH), three-band (detecting P. falciparum-antigen and Pv-pLDH) and four-band RDTs (detecting P. falciparum, Pv-pLDH and pan-pLDH).False positive Pv-pLDH lines were observed in 6/9 RDTs (including two- three- and four-band RDTs). They occurred in the individual RDT brands at frequencies ranging from 8.2% to 29.1%. For 19/85 samples, at least two RDT brands generated a false positive Pv-pLDH line. Sixteen of 85 (18.8%) false positive lines were of medium or strong line intensity. There was no significant relation between false positive results and parasite density or geographic origin of the samples.False positive Pv-pLDH lines in P. falciparum samples with high parasite density occurred in 6/9 P. vivax-specific RDTs. This is of concern as P. falciparum and P. vivax are co-circulating in many regions. The diagnosis of life-threatening P. falciparum malaria may be missed (two-band Pv-pLDH RDT), or the patient may be treated incorrectly with primaquine (three- or four-band RDTs).Malaria rapid diagnostic tests (RDTs) are immunochromatographic tests targeting antigens of one or more Plasmodium species. Signals are visible as cherry-red to purple coloured lines, comprising a control line (which indicates that the test has been performed well) and one or two test lines. The initially developed two band tests generate a test line that targets P. falciparum by detecting either histidine-rich protein 2 (HRP-2) or P. falciparum-specific parasite lactate dehydrogenase (Pf-pLDH). The later developed three band tests include a second target that is common to the four Plasmodium species, such as aldolase or pan-specific parasite lactate dehydrogenase (pan-pLDH). However, the conventional three-band RDTs, detecting a P. falciparum-specific antigen and a pan-Plasmodium a