Comparison of two simple methods for determining malaria parasite density.

Two simple methods for determining malaria parasite density which require only the examination of a thick blood film were compared with a more accurate method which involves determination of the red blood cell count and measurement of the level of infection in red blood cells by examination of a thin blood film. In one method, the number of parasites present per white blood cell is counted and this figure multiplied by 8000 (an average white blood cell count per microliter) to give the parasite density. In the other method, the number of parasites present per high power microscope field is determined and the parasite density calculated from this value and the assumed volume of blood present in one high power field. The latter method proved to be more accurate than that based on determination of the parasite/white blood cell ratio, probably because the variability in the volume of blood used in preparation of thick blood films was less than the variability of the white blood cell count in the population studied.