NEUTROPHIL-TO-LYMPHOCYTE AND PLATELET-TO-LYMPHOCYTE RATIOS ACROSS SCHIZOPHRENIA, BIPOLAR DISORDER, AND MAJOR DEPRESSIVE DISORDER: A COMPARATIVE CROSS-SECTIONAL STUDY

Abstract

Background: Peripheral immune dysregulation has been reported across schizophrenia and mood disorders, but cross-diagnostic evidence using inexpensive complete-blood-count-derived inflammatory ratios remains inconsistent. Medication exposure may further obscure disorder-related differences. Aim: To compare neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) among drug-naive and drug-free adults with schizophrenia, bipolar disorder, and major depressive disorder. Methods: This hospital-based comparative cross-sectional study included 90 adults aged 18-60 years: 30 with schizophrenia, 30 with bipolar disorder, and 30 with major depressive disorder. Diagnoses were established using ICD-11 criteria. Participants were either psychotropic-drug-naive or drug-free for at least 2 months after oral medication or 3 months after depot medication. Blood was collected in EDTA tubes and analyzed using an automated hematology analyzer. NLR and PLR were derived from the complete blood count. Group differences were assessed with one-way analysis of variance; effect sizes were expressed as η². Pairwise Welch contrasts were multiplicity-adjusted using the Holm method. Results: Mean NLR was 3.23 ± 0.10 in schizophrenia, 3.21 ± 0.50 in bipolar disorder, and 2.30 ± 0.10 in major depressive disorder. The overall difference was significant, F(2,87)=77.70, p<0.05, η²=0.641. NLR did not differ between schizophrenia and bipolar disorder (adjusted p=0.831), whereas both groups had higher NLR than major depressive disorder (adjusted p<0.05). Mean PLR was 138.4 ± 2.6, 131.6 ± 3.7, and 128.2 ± 2.1, respectively, with a significant overall difference, F(2,87)=94.60, p<0.05, η²=0.685; all pairwise PLR contrasts were significant after correction (adjusted p<0.05). Conclusions: Inflammatory ratios differed across the three diagnostic groups. Schizophrenia and bipolar disorder had comparable NLR values, while major depressive disorder had lower NLR. PLR showed a graded pattern, highest in schizophrenia and lowest in major depressive disorder. These unadjusted cross-sectional findings support a transdiagnostic inflammatory signal but do not establish diagnostic specificity or causality. Replication with healthy controls, larger samples, and multivariable adjustment is required.