Comparative evaluation of four techniques for the diagnosis of Plasmodium falciparum infections

Abstract

Four diagnostic techniques for Plasmodium falciparum infection were evaluated against serial parasite dilutions and on identical field samples. These were (i) Giemsa-stained thick blood films (GTF), (ii) acridine orange-stained thick (AOTF) and thin (AOTnF) blood films, (iii) the quantitative buffy coat technique (QBC^®); and (iv) the ParaSight ^TM-F dipstick test (PS). PS had a consistently higher sensitivity and speed, was easiest to learn, and required no laboratory facility. The 100% sensitivity cut-off points against known parasite densities (per mm³) were: PS, 30; GTF, 84; QBC^®, 84; AOTnF, 84; AOTF, 149. In the field study, test sensitivities compared with examination of 800 microscope fields of a Giemsa-stained thin blood film were PS, 96·6%; AOTF, 93·1%; GTF, 91·4%; QBC^®, 89·7%; AOTnF, 82·8%. In the dilution study, one false positive result was recorded with QBC^®; in the field study there was one false positive each with PS, AOTnF and AOTF. When a newly trained microscopist examined samples of the parasite dilutions, the 100% sensitivity cut-off points were AOTF, 84; GTF, 140; QBC^®, 390. Total handling time was shortest with PS regardless of whether samples were processed individually or in batches of 10 or 100. The ParaSight^TM-F test is recommended as the diagnostic tool for the future.