Previous research has demonstrated that malaria infected
RBCs differ in density compared to normal RBCs and are
enriched near the buffy coat. Furthermore, the microscopic
analysis of red blood cells from this fraction can increase the
sensitivity of microscopic detection of Plasmodium infected
RBCs[6-14].
In an effort to enhance the sensitivity of microscopic
analysis of blood films for the detection of malarial parasites,
we compared three methods of blood film preparation.
In the first method, blood films were made from whole
blood samples; in the second method, blood samples were
centrifuged in plastic micro-hematocrit tubes as described
in Materials and methods. In the third method, blood
was allowed to gravitationally sediment in plastic microhematocrit
tubes. In methods two and three the blood smear
was prepared from cells isolated near the buffy coat.
Results demonstrate that during the initial one minute
diagnostic scans of blood films, 25.37% of traditional blood
smears were identified as positive for the presence of
plasmodium infected RBCs. In samples where cells were
centrifuged or gravitationally sedimented, 30.24% of patient
samples were identified as positive for infected RBCs
(Figure 1). These results indicate that there is a statistically
significant increase in the sensitivity of malaria detection in
blood samples where parasitized cells have been enriched
through centrifugation or sedimentation. Importantly, the
observed increase in sensitivity was identical, regardless of
if the patient samples had been centrifuged or subjected to
passive gravitational sedimentation.
Results confirmed that centrifugation of blood samples
leads to a significant increase in assay sensitivity and that
passive gravitational sedimentation results in an equally
efficient detection rate. We next sought to determine the
percent parasitemia in samples prepared by each of the
three different methods of microscopic malaria detection.
Data indicate that centrifugation as well as sedimentation
of the blood samples resulted in a statistically significant
increase in the number of parasites counted per 1000 RBCs
when compared to traditional blood smear preparation
(P