On-site diagnosis of Plasmodium falciparum, P. vivax, and P. malariae by using the Quantitative Buffy Coat system

The Quantitative Buffy Coat (QBC) system was used for the detection and identification of malaria parasites in blood specimens from 570 residents of Oksibil, an isolated highland valley in the eastern Jayawijaya Mountains of Irian Jaya (Indonesian New Guinea). The availability of a battery-powered centrifuge and a fiberoptic Paralens enabled us to complete and interpret the assay in this remote environment. Of 322 QBC tubes examined for 2-4 min each, results of 295 (92%) concurred with findings on the matched Giemsa-stained thick smear (GTS). The 27 discrepant results included 13 QBC+/GTS- that, upon reexamination, were found to be GTS+. When using the corrected GTS results as the standard, the sensitivity and specificity of the QBC were 94% and 96%, respectively. Because electricity was available only 3 hr per day, it was decided to decrease the examination for an additional 248 QBC to a maximum of 90 sec per tube. This shortened inspection time resulted in a reduction of sensitivity to 53% but specificity was preserved at 89%. Forty-two of 45 conflicting results, QBC-/GTS+ from cases of light Plasmodium falciparum infections with < 1 trophozoite or gametocyte per field, were resolved by reexamination of the QBC in the laboratory. Tubes held at 4 C could be reexamined, without noticeable loss of fluorescence, for at least 6 wk after collection. Despite some difficulty in the identification of Plasmodium species, it was concluded that the QBC is an easy, sensitive method for the rapid diagnosis of malaria in the field and that it provides the inexperienced microscopist with an additional means for on-site identification of individuals needing treatment.