Pan-Plasmodium band sensitivity for Plasmodium falciparum detection in combination malaria rapid diagnostic tests and implications for clinical management

Abstract

BackgroundMalaria rapid diagnostic tests (RDTs) are appropriate for case management, but persistent antigenaemia is a concern for HRP2-detecting RDTs in endemic areas. It has been suggested that pan-pLDH test bands on combination RDTs could be used to distinguish persistent antigenaemia from active Plasmodium falciparum infection, however this assumes all active infections produce positive results on both bands of RDTs, an assertion that has not been demonstrated.MethodsIn this study, data generated during the WHO-FIND product testing programme for malaria RDTs was reviewed to investigate the reactivity of individual test bands against P. falciparum in 18 combination RDTs. Each product was tested against multiple wild-type P. falciparum only samples. Antigen levels were measured by quantitative ELISA for HRP2, pLDH and aldolase.ResultsWhen tested against P. falciparum samples at 200 parasites/μL, 92% of RDTs were positive; 57% of these on both the P. falciparum and pan bands, while 43% were positive on the P. falciparum band only. There was a relationship between antigen concentration and band positivity; ≥4 ng/mL of HRP2 produced positive results in more than 95% of P. falciparum bands, while ≥45 ng/mL of pLDH was required for at least 90% of pan bands to be positive.ConclusionsIn active P. falciparum infections it is common for combination RDTs to return a positive HRP2 band combined with a negative pan-pLDH band, and when both bands are positive, often the pan band is faint. Thus active infections could be missed if the presence of a HRP2 band in the absence of a pan band is interpreted as being caused solely by persistent antigenaemia.

Plasmodium falciparum Parasitemia and Band Sensitivity of the SD Bioline Malaria Ag P.f/Pan Rapid Diagnostic Test in Madagascar

“…Together, these results are consistent with those previously reported using the same RDT. 13,14 Furthermore, similar patterns were also reported for other similar products, such as the CareStart Malaria HRP2/ pLDH (Pf/pan) Combo RDT, 30 and for a different, P. falciparumspecific SD Malaria Ag P.f (05FK90) product, which targets PfHRP2 and Pf-pLDH. 31 Among the samples that were diagnosed as P. falciparum-only infections by microscopy, there were P. falciparum mixed infections as detected by LDR-FMA; a number of them were P. falciparum-P. vivax mixed infections ( Table 2).…”

“…In addition, even when both PfHRP2 and pan bands (pLDH or aldolase) were positive, the intensity of the pan band was lower than that of the PfHRP2 band. 13,14,30,31 Both band intensities (visually scored, five categories) were correlated with parasite densities, with considerable overlap between categories. 13,14,30 Faint bands are often difficult to see and may be missed by health workers in reduced lighting conditions or with reduced visual acuity.…”

“…13,14,30,31 Both band intensities (visually scored, five categories) were correlated with parasite densities, with considerable overlap between categories. 13,14,30 Faint bands are often difficult to see and may be missed by health workers in reduced lighting conditions or with reduced visual acuity. 13 This may inflate the proportion of RDTs reported as having a positive PfHRP2 band and negative pan band.…”

“…13,14,30 Faint bands are often difficult to see and may be missed by health workers in reduced lighting conditions or with reduced visual acuity. 13 This may inflate the proportion of RDTs reported as having a positive PfHRP2 band and negative pan band.…”

“…Among these are very low or high parasite densities/target antigen concentrations. 12,13 A recent WHO-FIND product testing study 13 analyzed 18 combination RDT products for PfHRP2 and pan band (17 pLDH and one aldolase) positivity against a panel of approximately 100 P. falciparum parasite samples, which were collected from patients with active, PCRconfirmed P. falciparum mono-infections and without a history of antimalarial therapy in the month preceding the analysis. Tests were performed using each sample diluted to 200 and 2,000 or 5,000 parasites/μL densities.…”