Eosinopenia as a diagnostic marker of bloodstream infection in a general internal medicine setting: A cohort study

Abstract Background Little is known about the potential use of the eosinophil count as a predictive marker of bloodstream infection. In this study, we aimed to assess the reliability of eosinopenia as a predictive marker of bloodstream infection. Methods This study was a retrospective cohort study. The outpatient department and general internal medicine department of a tertiary university hospital in Japan. A total of 189 adult patients with at least 2 sets of blood cultures obtained during January 1–December 31, 2018, after excluding those with the use of antibiotic therapy within 2 weeks prior to blood culture, steroid therapy, a history of haematological cancer, or eosinophilia. The diagnostic accuracies of each univariate variable and the multivariable logistic regression models were assessed by calculating the areas under the receiver operating characteristic curves (AUROCs). The primary outcome was a positive blood culture indicating bloodstream infection. Results Severe eosinopenia (<10 cells/mm3) alone yielded little overall predictive ability (AUROC: 0.606, 95% confidence interval (CI): 0.502–0.710, P=0.035), and only moderate sensitivity (50%, 95%CI: 29–70%) and specificity (71%, 95%CI: 63–78%). The model comprising baseline variables (age, sex) and the C-reactive protein level yielded an AUROC of 0.7384, and the further addition of eosinopenia yielded a slight improvement, with an AUROC of 0.7547 (P=0.4297) and a statistically significant net reclassification improvement (NRI) (P=0.03). However, the integrated discrimination index (IDI) (P=0.282) remained non-significant. Conclusions Severe eosinopenia can be considered an inexpensive marker of bloodstream infection in a general internal medicine setting.