Malaria rapid diagnostic tests: Plasmodium falciparum infections with high parasite densities may generate false positive Plasmodium vivax pLDH lines.
BACKGROUND
Most malaria rapid diagnostic tests (RDTs) detect Plasmodium falciparum and an antigen common to the four species. Plasmodium vivax-specific RDTs target P. vivax-specific parasite lactate dehydrogenase (Pv-pLDH). Previous observations of false positive Pv-pLDH test lines in P. falciparum samples incited to the present study, which assessed P. vivax-specific RDTs for the occurrence of false positive Pv-pLDH lines in P. falciparum samples.


METHODS
Nine P. vivax-specific RDTs were tested with 85 P. falciparum samples of high (>or=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).


RESULTS
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.


CONCLUSIONS
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).
Maltha
Jessica
J
Faculty of Health, Medicine and Life Sciences FHML, Maastricht, The Netherlands. j.maltha@student.maastrichtuniversity.nl
Gillet
Philippe
P
Cnops
Lieselotte
L
van den Ende
Jef
J
van Esbroeck
Marjan
M
Jacobs
Jan
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000953:Antigens, Protozoan / Q000032:analysis / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D002845:Chromatography; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D016778:Malaria, Falciparum / Q000175:diagnosis* / Q000469:parasitology; D016780:Malaria, Vivax / Q000175:diagnosis* / Q000469:parasitology; D008297:Male; D008853:Microscopy; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification*; D010966:Plasmodium vivax / Q000235:genetics* / Q000276:immunology; D016133:Polymerase Chain Reaction; D011933:Reagent Kits, Diagnostic; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult
D000953:Antigens, Protozoan; D011933:Reagent Kits, Diagnostic; D007770:L-Lactate Dehydrogenase