Rapid Diagnostic Tests Evaluated for Pregnancy Malaria

Rapid diagnostic tests (RDTs) are an ideal diagnostic complement to microscopy, due to their ease of use and adequate sensitivity in detecting even submicroscopic infections.

Scientists at the National Institute of Medical Research (Tanga, Tanzania) collaborated with other international centers to evaluate the immunochromatographic RDTs under field conditions. A cohort of 924 pregnant women was followed up from enrolment until delivery, and a total of 5,905 samples were collected. Of those, 5,167 venous and 388/650 placental blood samples, for which there were complete RDT and microscopy datasets, were randomly selected for analysis.

The accuracy and reliability of RDTs in diagnosing PAM was evaluated using microscopy and nested polymerase chain reaction (PCR). Venous and placental blood samples evaluated by histidine rich protein 2 (HRP-2) and parasite lactate dehydrogenase (pLDH) based RDT Parascreen, (Zephyr Biomedicals; Goa, India) or HRP-2 only RDTs Paracheck Pf (Orchid Biomedical Systems; Mumbai, India) and ParaHITf (Span Diagnostics Ltd.; Surat, India).

Overall 91 of 5,555 (1.6%) samples were positive for malarial parasite antigen based on RDTs, whereas 49 of 5,555 (0.9%) were positive by microscopy. Of the 91 RDT positive samples, 50.5% were microscopy positive, while 49.5% were microscopy negative. To test whether the 45 microscopy negative but RDT positive samples were genuinely negative or false positive, a species diagnostic PCR assay was performed. Intriguingly, 19 of the 45 (42.2%) microscopy negative were positive by PCR and only three samples were positive by microscopy but negative by RDT.

The authors concluded that RDTs outperform expert microscopy in detecting asymptomatic Plasmodium falciparum in pregnant women. Given the difficulties in establishing reliable microscopy based diagnostic services, RDTs are good alternative for the detection and in the management of malaria infections in pregnant women. RDTs can both be used to detect infections not cleared by intermittent preventive treatment during pregnancy (IPTp) or to detect infections where the malaria endemicity is too low to warrant IPTp. The study was published on June 21, 2012, in the Malaria Journal .

Related Links:
Tanzania National Institute of Medical Research
Zephyr Biomedicals
Orchid Biomedical Systems