The utility of extended differential parameters as a biomarker of bacteremia at a tertiary academic hospital in persons with and without HIV infection in South Africa

INTRODUCTION: Extended differential parameters (EDPs) are generated with the automated differential count by Sysmex XN-series automated hematology analysers, and include the immature granulocyte count (IG%), the neutrophil fluorescent light intensity (NE-SFL) and the neutrophil fluorescent light distribution width (NE-WY). These have been proposed as early biomarkers of bacteremia. This study aimed to evaluate the NE-SFL, NE-WY and IG% in comparison to neutrophil CD64 (nCD64) expression (as a high quality sepsis biomarker) among patients with suspected bacterial sepsis at the Chris Hani Baragwanath Academic Hospital in Johannesburg, South Africa. METHODS: A daily search of the laboratory information system identified samples submitted for a blood culture (BC) and a concurrent full blood count (FBC). Automated differential counts using a Sysmex XN-9000 haematology analyser and neutrophil CD64 expression by flow cytometry were assessed on the residual FBC samples. RESULTS: A total of 151 samples were collected, of which 83 were excluded due to equivocal results with regards to the presence of bacterial infection. The remaining 68 samples included 23 with bacteremia, 28 with evidence of non-bacteremic bacterial infection, 13 with no evidence of bacterial infection and 4 with Tuberculosis. HIV status was documented in 90 of the patients, with a seropositivity rate of 57.8%. The EDPs were all significantly higher among patients with bacteremia as compared to those without bacterial infection, but on ROC curve analyses, only the NE-SFL showed good performance (AUC>0.8) for discriminating cases with bacteremia from those without bacterial infection at a cut-off value of 49.75. In comparison to the nCD64, the NE-SFL showed moderate agreement (kappa = 0.5). On stratification of the ROC analysis by HIV status, the NE-SFL showed superior performance among persons with HIV infection (AUC = 1), while the automated IG% showed better performance among the patients without HIV infection (AUC = 0.9). CONCLUSION: In this study, EDPs showed differential performance as biomarkers for bacteremia according to HIV-status in the South African setting, with the most promising results seen with the NE-SFL and IG% parameters among people with and without HIV infection, respectively. Further assessment of these parameters without pre-selection of patients likely to have infection is required to further determine their clinical utility, particularly among patients with underlying inflammatory conditions or malignancy.