Complete Blood-Count-Derived Inflammatory Markers Across Acute Mood Episodes

Background: Recent evidence has suggested that low-grade systemic inflammation may contribute to the clinical expression of mood disorders, yet findings have differed considerably across studies. The present study compared several complete blood-count (CBC)-derived inflammatory indices among inpatients with bipolar disorder (BD), manic and depressive episodes, and major depressive disorder (MDD), and examined whether psychotropic medications influenced these inflammatory markers. Methods: This retrospective chart-review study included only inpatients hospitalized with a diagnosis of BD or MDD between January 1, 2019, and January 1, 2023. A healthy control (HC) group, matched by age and sex, was included for comparison. For data independence, only the first CBC obtained within 24 hours of admission was analyzed. Inflammatory markers, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII), were calculated from standardized fasting blood samples. Statistical analyses were performed using the Kruskal-Wallis test for group comparisons, followed by Bonferroni-corrected Mann-Whitney U tests. Additionally, analysis of covariance (ANCOVA) and regression models were employed to control for potential confounders such as age, sex, length of stay, and various psychotropic medications (lithium, antidepressants, and antipsychotics). Results: NLR and MLR ratios were consistently higher in all mood-disorder groups than in healthy individuals. PLR elevation appeared specific to the MDD group, and the SII was increased in depressive episodes but not in mania. These patterns remained statistically significant after adjustment for demographic covariates; male sex was negatively associated with PLR. Regression analyses adjusted for age and sex demonstrated a negative association between antidepressant use and PLR and MLR values. Conclusions: These results suggested that acute mood episodes are accompanied by measurable increases in certain inflammation-related hematologic markers. The inverse relationship between antidepressant use and PLR and MLR was consistent with an association between medication use and nonspecific systemic inflammatory markers observed in acutely hospitalized patients.