Platelet and white blood-cell-based ratios: Differential inflammatory markers of severe mental disorders?

Neutrophil/lymphocyte (NLR), monocyte/lymphocyte (MLR), and platelet/lymphocyte (PLR) ratios, and systemic inflammatory index (SII) represent peripheral markers of inflammation associated with different severe mental disorders. In this study, these parameters were analyzed in a sample of 622 participants [197 patients with major depressive disorder (MDD), 154 with bipolar disorder (BD), 176 with schizophrenia (SCH), and 95 healthy controls (HC)]. Sociodemographic and clinical data of patients were recorded. Differences in age and sex were detected among groups (p < 0.001), with SCH patients being younger and MDD patients being older. After stratifying by sex, these ratios were compared using the nonparametric ANCOVA (Quade's test) using age as a covariate. In males, no significant statistical differences were found between groups. However, differences were observed in MLR in the subgroup of females [MDD: 0.23 (SD = 0.09); BD: 0.23 (SD = 0.11); SCH: 0.24 (SD = 0.11); HC: 0.29 (SD = 0.13); F = 5.376, p = 0.001]. Post hoc testing revealed that there are MLR differences between HC versus MDD and between HC versus BD, with higher values in HC versus the other two groups. On the other hand, no differences were found in either males or females for any of the studied ratios, among the three diagnostic groups. MLR is reduced in MDD and BD patients versus HC, but exclusively in the female group. However, based on the analyzed indices, it is not possible to differentiate among the three diagnostic groups of patients. As a limitation of this study, note that the effects of psychopharmacological treatments and smoking have not been controlled for.