Avaliação de diferentes métodos de quantificação microscópica da parasitemia de pacientes portadores de malária aguda da Amazônia brasileira

Abstract

The estimation of malaria parasite density is important to define disease severity and to evaluate the in vivo therapeutic response. Since errors could be introduced in the estimation techniques, we outlined the present study to analyse different methods of quantification and different values of leukocytes counting that can be assumed as the basis of calculation for the estimation. The reference parasitemia was estimated using automated leukocyte counting. The study included patients with confirmed diagnosis of malaria and of which was evaluated by hematological blood count. The estimation of parasitemia reference was made by the ratio between the average number of parasites counted in 500 leukocytes, taking the automated countin as basis for calculating. In addition, estimates were also made based on the assumed fixed value of 8000 leukocytes/uL and on the volume of blood in a given microscopic area. These methods are recommended by WHO for areas where the laboratorial leukocyte it is not available counting. Other fixed values of leukocytes were also analyzed to identify the number of assumed leukocytes that best estimates the parasitemia. The results showed that the fixed value of 8000 leukocytes/uL overestimates parasitemia. The high proportion of adults in the sample and not considering the age of the patient were probably the reasons for this overestimation. Moreover, the parasitemia was underestimated when measured by the method that assumes a fixed volume of blood in the examined microscopic smear area, probably related to errors in preparation of the blood smear. The assumed values of leukocytes which showed better agreement whit the actual patient parasitemia were 5,250 and 5,500 leukocytes/uL, consistent with the profile of leukocytes revealed by the sample and with the standard reference for people in Brazil and South America, which is close to these values. Thus, it is plausible to assume that fixed values between 5,000 and 6,000 leukocytes/uL better estimate the parasitemia of patients with malaria in the Brazilian Amazon, in areas where laboratory measurement is not available.