Performance of Malaria Rapid Diagnostics Tests Evaluated Post-Treatment

The number of different RDTs on the market has increased considerably over the past few years and most malaria RDTs are designed to detect a single parasite antigen, the histidine-rich protein 2 (HRP2) or the Plasmodium lactate dehydrogenase (pLDH), while others are designed to detect both antigens in a single test.

Scientists at the Epicentre Mbarara Research Centre (Uganda) recruited consecutively all children who presented to any of the participating health centers, were under five years of age, weighed 5 kg or more, and had a fever. Blood samples obtained by finger prick from children whose parent or guardian provided written consent were tested in parallel at the corresponding study health center with the three different RDTs and with microscopy. At each site, a sub-set of 212 children was selected for the time to become negative analysis.

The following RDTs were evaluated: SD Bioline Malaria Antigen P.f (HRP2) (Standard Diagnostic Inc, Suwon, South Korea), CareStart Malaria HRP2 (Pf), and CareStart Malaria pLDH (PAN) (Access Bio, Somerset, NJ, USA). For microscopy, thick and thin blood smears were prepared on the same slide and stained with a 10% Giemsa solution (pH 7.2) for 15 minutes. Reading was performed using a 100× magnification lens with oil immersion. Parasite density was estimated based on a hypothetical leukocyte density of 8,000 WBC/µL. The presence of gametocytes was recorded, although a slide with gametocytes but no asexual parasite forms was scored as negative.

The team reported that the median time to become negative was 35 and 42 days for the SD Bioline HRP2 in two different sites, and two days for the CareStart pLDH at both sites. For the CareStart HRP2 test, the median time could not be calculated because it exceeded 42 days, the maximum follow-up time for patients in the study. In the two settings, sensitivities ranged from 98.4% to 99.2% for the HRP2 tests and 94.7% to 96.1% for the pLDH test. Specificities were 98.9% and 98.8 % for the HRP2 tests and 99.7 % for the pLDH test in the low-transmission setting and 79.7%, 80.7% and 93.9 %, respectively, in the high-transmission setting.

The authors concluded that the ideal malaria RDT, a test that is both highly sensitive and highly specific in all epidemiological contexts is not yet available. A choice is to be made between an HPR2 test, with the risk of over diagnosing malaria and thereby overlooking other possible causes of fever, and using a pLDH test, which carries the risk of missing true malaria cases with low parasitemia. The study was published on October 4, 2016, in the Malaria Journal.

Related Links:
Epicentre Mbarara Research Centre
Standard Diagnostic
Access Bio