Eosinophils to Lymphocytes Ratio (ELR) as a Potential Inflammatory Biomarker in Patients with Dual Diagnosis of Bipolar and Alcohol Use Disorders: A Retrospective Cohort Study

Objective: It is well-established that Bipolar Disorder (BD) has comorbidity with Alcohol Use Disorder (AUD) and could present the same symptoms of an underlying diagnosis of BD, therefore delaying the proper relevant treatment. Recent studies show the occurrence of alterations in the circulating levels of inflammatory mediators in patients dealing with AUD as well as those with BD. The objective of this study is to get an assessment of whether patients with AUD and BD comorbidity [BD(+)] would present different ratios of the Complete Blood Count (CBC) in comparison with patients with AUD but without a BD comorbidity [BD(-)]. Methods: This is a retrospective study, conducted through a selection of patients files who were admitted to the psychiatric department at Hôtel-Dieu de France University Hospital in Beirut, Lebanon, between January of the year 2016 and May of the year 2021. Overall, 83 files of patients dealing with AUD were included in this study. Results: Patients with BD(+) showed a higher Eosinophils to Lymphocytes Ratio (ELR) in comparison to those with BD(-). The Receiver Operation Characteristic (ROC) analysis had an area under the curve at 0.719 with a p = .001. The cutoff value of ELR that best differentiates BD(-) from BD(+) was 0.087 (Sensitivity = 81.3%; Specificity = 63.6%). The logistic regression analysis showed that an ELR superior to 0.087 presented a statistically significant difference, exposing patients belonging to the BD(+) group (OR = 11.66; p < .001). Conclusions: Our data suggest that ELR may be a valuable, reproducible, easily accessible, and cost-effective inflammatory marker, pointing at the presence of a BD comorbidity with AUD.