Association of Leukocyte Subpopulations Identified by Flow Cytometry with Outcomes of Sepsis in a Respiratory Intensive Care Unit: An Observational Study

Introduction The dysregulated host immune response in sepsis is orchestrated by peripheral blood leukocytes. This study explored the associations of the peripheral blood leukocyte subpopulations with early clinical deterioration and mortality in sepsis. Methods We performed a prospective observational single-center study enrolling adult subjects with sepsis within 48 h of hospital admission. Peripheral blood flow cytometry was performed for the patients at enrolment and after 5 days. The primary outcome was to explore the association between various leukocyte subpopulations at enrolment and early clinical deterioration [defined as an increase in the sequential organ failure assessment (SOFA) score between enrolment and day 5, or death before day 5]. Other pre-specified outcomes explored associations of leukocyte subpopulations at enrolment and on day 5 with in-hospital mortality. Results A total of 100 patients, including 47 with septic shock were enrolled. The mean (SD) age of the patients was 53.99 (14.93) years. Among them, 26 patients had early clinical deterioration, whereas 41 died during hospitalization. There was no significant association between the leukocyte subpopulations at enrolment and early clinical deterioration on day 5. On multivariate logistic regression, a reduced percentage of CD8 + CD25+ T-cells at enrolment was associated with in-hospital mortality [odds ratio (OR), 0.82 (0.70-0.97); p-value = 0.02]. A reduced lymphocyte percentage on day 5 was associated with in-hospital mortality [OR, 0.28 (0.11-0.69); p-value = 0.01]. In a post-hoc analysis, patients with "very early" deterioration within 48 h had an increased granulocyte CD64 median fluorescent intensity (MFI) [OR, 1.07 (1.01-1.14); p-value = 0.02] and a reduced granulocyte CD16 MFI [OR, 0.97 (0.95-1.00); p-value = 0.04] at enrolment. Conclusions None of the leukocyte subpopulations showed an association with early clinical deterioration at day 5. Impaired lymphocyte activation and lymphocytopenia indicative of adaptive immune dysfunction may be associated with in-hospital mortality.