[Diagnostic test to identify human Plasmodium species by the quantitative buffy coat test]

The quantitative buffy coat system (QBC Test) was designed for rapid diagnosis of malaria by identifying the presence of hemoparasites. The main drawback of the technique is failure to identify the Plasmodium species. The purpose of this study was to attempt to remedy this problem by studying the distribution of the parasites at the bottom of the test tube. Indeed since the QBC Test is based on gradient centrifugation of blood components, the distribution of the parasites in the test tube depends on density. Blind QBC Tests were performed on specimens obtained from two different batches, i.e., one from France and the other from Burkina Faso. Distribution curves were obtained by counting the number of parasites in all microscopic fields in the five-millimeter test tube. Our findings showed differences in distribution curve depending on species. For Plasmodium falciparum, the number of parasites was nearly the same in all fields suggesting that the arrangement of the parasites in the QBC Test tube was linear. For Plasmodium vivax and Plasmodium ovale, the number of parasites was markedly lower near the cap of the tube suggesting that a non-linear arrangement with a decreasing number of parasites toward the top of the tube. In 97 p. 100 of cases, we were able to propose a differential diagnosis of Plasmodium falciparum versus Plasmodium vivax or Plasmodium ovale. However it was not possible to distinguish between Plasmodium vivax and Plasmodium ovale. In case of mixed infection it would be difficult to distinguish Plasmodium falciparum from the other species. The ability to identify Plasmodium species would add to the advantages of the rapid and sensitive QBC Test.