Acridine orange detection of Plasmodium falciparum malaria: relationship between sensitivity and optical...

Blood samples collected from five volunteers participating in a P. falciparum infectivity trial were examined to determine the efficacy of the acridine orange technique. Several lens configurations were tested for efficiency in the diagnosis of malaria using this system. There was no significant difference in the sensitivity for detecting positive specimens or number of parasites among three lens configurations: a 50x long working distance objective (0.34 mm) with either a 10x ocular (total magnification 500x) or a 12.5x ocular (625x) and a 750x configuration using a 50x objective with a shorter working distance (0.24 mm). All three lens configurations were significantly better than the 1,000x configuration using a commonly available 100x oil immersion objective. The results achieved using this lens still exceeded the sensitivity of the thick blood film.