Evaluation of haematological and volume, conductivity and scatter parameters of leucocytes for aetiological diagnosis of undifferentiated fevers

Background: In this follow-up study, we aimed to establish the cut-off values of the volume, conductivity and scatter (VCS) parameters of leucocytes that significantly differ in dengue fever, malaria, scrub typhus and enteric fever, as described in our pilot study. Methods: A prospective observational case-control study was undertaken on patients with an established diagnosis of acute malaria (n=476), dengue fever (n=927), scrub typhus (n=425), bacterial sepsis (n=1598) or enteric fever (n=885) and the haematological and VCS data obtained by the Coulter LH 750 analyser were compared with controls. Results: Malaria significantly altered the platelet count and plateletcrit. The cut-offs for the monocyte volume, lymphocyte volume, neutrophil volume, neutrophil volume distribution width, lymphocyte volume distribution width, monocyte volume distribution width and neutrophil conductivity distribution width had 90% negative predictive values (NPVs) for malaria. Except for the proportion of monocytes, lymphocyte scatter distribution width and platelet distribution width, a > 70% positive (PPV) and negative predictive value (NPV) for dengue was noted in all the haematological and VCS parameters analysed. While the cut-offs determined in scrub typhus had a good (> 80%) PPV and NPV, a significant difference was seen in neutrophil, monocyte and lymphocyte conductivities, but with low sensitivity, specificity, PPV and NPV in enteric fever. Conclusions: Aetiology-specific changes occur both in numbers as well as in VCS properties in acute fevers. Formulae and/or algorithms need to be utilized to realize the full potential of the VCS technology.