Assumed White Blood Cell Count of 8,000 Cells/μL Overestimates Malaria Parasite Density in the Brazilian Amazon

Abstract

Quantification of parasite density is an important component in the diagnosis of malaria infection. The accuracy of this estimation varies according to the method used. The aim of this study was to assess the agreement between the parasite density values obtained with the assumed value of 8,000 cells/μL and the automated WBC count. Moreover, the same comparative analysis was carried out for other assumed values of WBCs. The study was carried out in Brazil with 403 malaria patients who were infected in different endemic areas of the Brazilian Amazon. The use of a fixed WBC count of 8,000 cells/μL to quantify parasite density in malaria patients led to overestimated parasitemia and resulted in low reliability when compared to the automated WBC count. Assumed values ranging between 5,000 and 6,000 cells/μL, and 5,500 cells/μL in particular, showed higher reliability and more similar values of parasite density when compared between the 2 methods. The findings show that assumed WBC count of 5,500 cells/μL could lead to a more accurate estimation of parasite density for malaria patients in this endemic region.

A more appropriate white blood cell count for estimating malaria parasite density in Plasmodium vivax patients in northeastern Myanmar

“…Nonetheless, this notion has been repeatedly observed in similar studies conducted in other malaria-endemic regions (Table 4). Of particular notice is that despite regional difference, the assumed WBC count of 5,500 cells/µl from this study coincided well with the proposed WBC count in a region of the Brazilian Amazon, where the majority (92.6%) of the study subjects was adults (Alves-Junior et al, 2014). An assumed WBC count of 5,000 cells/µl for patients five years and older matched well with a recent finding in south-western India, where all patients were adults and infected with P. vivax only (Rishikesh et al, 2015).…”

“…The World Health Organization (WHO) recommended the use of an assumed WBC value of 8,000/µl (WHO, 2010), which was based on a study with a Nigerian population with a large proportion of children younger than five years (Dowling and Shute, 1966). Yet, recent studies found that estimating malaria parasite densities using this WBC value yielded results that were inconsistent with the actual observed malaria parasite density of patients in some areas (Alves-Junior et al, 2014; Jeremiah and Uko, 2007; McKenzie et al, 2005; Rishikesh et al, 2015). Furthermore, whereas most studies conducted so far focused on P. falciparum patients, studies conducted in areas co-endemic for P. vivax and P. falciparum revealed considerable differences in WBC counts between patients infected with these two parasite species (Alves-Junior et al, 2014; McKenzie et al, 2005).…”

“…Yet, recent studies found that estimating malaria parasite densities using this WBC value yielded results that were inconsistent with the actual observed malaria parasite density of patients in some areas (Alves-Junior et al, 2014; Jeremiah and Uko, 2007; McKenzie et al, 2005; Rishikesh et al, 2015). Furthermore, whereas most studies conducted so far focused on P. falciparum patients, studies conducted in areas co-endemic for P. vivax and P. falciparum revealed considerable differences in WBC counts between patients infected with these two parasite species (Alves-Junior et al, 2014; McKenzie et al, 2005). Since the abundance of WBCs is influenced by the host immune status (Berens-Riha et al, 2014), and may vary in people of different races, ages, nutritional conditions, and pathogen infections, the baseline values of leukocytes in patients may differ significantly between populations and geographical regions (Bain, 1996).…”

“…Since the abundance of WBCs is influenced by the host immune status (Berens-Riha et al, 2014), and may vary in people of different races, ages, nutritional conditions, and pathogen infections, the baseline values of leukocytes in patients may differ significantly between populations and geographical regions (Bain, 1996). Therefore, it has been suggested that the best solution for estimating parasite densities is to use different WBC counts for different geographical regions, age groups and sub-populations (e.g., pregnant women), and epidemiological settings (Adu-Gyasi et al, 2012; Alves-Junior et al, 2014; Haggaz et al, 2014). …”

Hematological Indices in Malian Children Change Significantly During a Malaria Season and with Increasing Age: Implications for Malaria Epidemiological Studies

“…A similar recommendation was recently made for malaria patients in the Brazilian Amazon, where an assumed WBC count of 5,500/μL (instead of 8,000/μL) was shown to more accurately estimate parasite density. 21 Second, it may be difficult to establish a single reference interval for hematological indices in healthy African children. For example, in children aged 6-12 years, the median Ht that we observed in Mali (36.7-40.1%) was higher or similar to that reported in Uganda (34.4%) 16 or Tanzania (38.4%), 17 Finally, our study has several strengths and limitations.…”