Assessment of the prozone effect in malaria rapid diagnostic tests

Department of Clinical Sciences, Institute of Tropical Medicine (ITM), Nationalestraat 155, B 2000 Antwerp, Belgium.
Malaria Journal (Impact Factor: 3.11). 11/2009; 8(1):271. DOI: 10.1186/1475-2875-8-271
Source: PubMed


The prozone effect (or high doses-hook phenomenon) consists of false-negative or false-low results in immunological tests, due to an excess of either antigens or antibodies. Although frequently cited as a cause of false-negative results in malaria rapid diagnostic tests (RDTs), especially at high parasite densities of Plasmodium falciparum, it has been poorly documented. In this study, a panel of malaria RDTs was challenged with clinical samples with P. falciparum hyperparasitaemia (> 5% infected red blood cells).
Twenty-two RDT brands were tested with seven samples, both undiluted and upon 10 x, 50 x and 100 x dilutions in NaCl 0.9%. The P. falciparum targets included histidine-rich protein-2 (HRP-2, n = 17) and P. falciparum-specific parasite lactate dehydrogenase (Pf-pLDH, n = 5). Test lines intensities were recorded in the following categories: negative, faint, weak, medium or strong. The prozone effect was defined as an increase in test line intensity of at least one category after dilution, if observed upon duplicate testing and by two readers.
Sixteen of the 17 HRP-2 based RDTs were affected by prozone: the prozone effect was observed in at least one RDT sample/brand combination for 16/17 HRP-2 based RDTs in 6/7 samples, but not for any of the Pf-pLDH tests. The HRP-2 line intensities of the undiluted sample/brand combinations with prozone effect (n = 51) included a single negative (1.9%) and 29 faint and weak readings (56.9%). The other target lens (P. vivax-pLDH, pan-specific pLDH and aldolase) did not show a prozone effect.
This study confirms the prozone effect as a cause of false-negative HRP-2 RDTs in samples with hyperparasitaemia.

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Available from: Marcella Mori, Oct 04, 2015
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    • "Understanding genetic variation among vector populations is important for designing effective strategies to control vector-borne diseases via integrated vector control and/or anti-vector vaccination strategies (Dai et al., 2009; Gillet et al., 2009). R. appendiculatus has a wide distribution across eastern, central and southern Africa where it is a vector of several pathogens of veterinary and economic importance (De Vos, 1981; Perry et al., 1990; Walker et al., 2003). "
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    Ticks and Tick-borne Diseases 08/2015; DOI:10.1016/j.ttbdis.2015.08.001 · 2.72 Impact Factor
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    • "Firstly, manufacturer recommendations on the appropriate sample volume to be applied should always be followed, as application of too large a volume can elicit the phenom‐ enon. [58] The prozone effect is also abated upon dilution of the patients' samples, and so for patients presenting severe clinical manifestations of malaria, health care workers can elect to verify a weak or negative test result using a diluted sample. [60] Finally, the use of alternative device architectures may prevent the occurrence of the prozone effect. "
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    ABSTRACT: Immunochromatographic rapid diagnostic tests (RDTs) have demonstrated significant potential for use as point-of-care diagnostic tests in resource-limited settings. Most notably, RDTs for malaria have reached an unparalleled level of technological maturity and market penetration, and are now considered an important complement to standard microscopic methods of malaria diagnosis. However, the technical development of RDTs for other infectious diseases, and their uptake within the global health community as a core diagnostic modality, has been hindered by a number of extant challenges. These range from technical and biological issues, such as the need for better affinity agents and biomarkers of disease, to social, infrastructural, regulatory and economic barriers, which have all served to slow their adoption and diminish their impact. In order for the immunochromatographic RDT format to be successfully adapted to other disease targets, to see widespread distribution, and to improve clinical outcomes for patients on a global scale, these challenges must be identified and addressed, and the global health community must be engaged in championing the broader use of RDTs.
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    • "It has also been speculated that the variation in PfHRP2 sequences in samples from the Central African Republic might reduced the sensitivity of RDTs for detecting malaria at very low parasite density [29]. Other factors, such as the ‘prozone effect’ for Paracheck™-Pf at high parasite densities [55] and the presence of anti-HRP 2 in humans [22], might explain why some tests give negative results despite significant parasitaemia. "
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