Discriminant values for differentiation between malaria and non-malaria illness by hematology analyzer

Abstract

At present, technology of hematology analyzers has been improved. Of the advanced technologies, the VCS technology, the measurement of volume (V), conductivity (C) and light scatter (S), is introduced. Parameters obtained from this technology include mean and standard deviation (SD) for V, C, and S of each type of leukocytes. It has been demonstrated by some investigators that the discriminant factor (D) derived from these parameters can effectively discriminate malaria patients from normal individuals. However, information on its effectiveness for screening of malaria among febrile patients is not available.  In order to assess the effectiveness of the D value, 365 febrile patients suspected for malaria infection attending medical care service at PhobPhraHospital, Tak province, were recruited. All patients were investigated for hematological parameters using the Beckman Coulter® LH 750. Malaria was diagnosed according to the presence of malarial parasites on either thick or thin blood films. Of the 365 patients, 191 (52.3%) were positive for malaria. Of these, 112 were positive for P. falciparum, and 79 were positive for P.vivax. Analysis of hematological parameters showed that white blood cell count, red blood cell count, platelet count, hemoglobin level, and hematocrit values in malaria-infected group were significantly lower than those of non-infected group (P < 0.01). A marked reduction of platelet count was observed in malaria-infected group, i.e 122.1 ± 98.3 x 10⁹/l in malaria group, and 282.6 ± 102.4 x 10⁹/l in non-infected group. Determination of appropriate cutoff using ROC curve analysis revealed that a D value > 4.71 provided the highest effectiveness with a sensitivity of 78.5 % and specificity of 65.5 % (AUC = 0.7969).  Additional evaluation using platelet count < 150 as indicator, a better result was obtained with a sensitivity of 95.4 % and specificity of 72.8 % (AUC = 0.901). The findings indicate that platelet is an effective indicator for screening of malaria among febrile patients, and might be applicable to other endemic areas for malaria.