Role of depression, suicide attempt history and childhood trauma in neutrophil-to-lymphocyte ratio dynamics: A 30-week prospective study

Studying the biology of suicidal behaviour and developing blood-based biomarkers may help stratify individuals with suicidal behaviors into clinically relevant categories. Literature suggests that people diagnosed with mood disorders and suicidal behaviour show an increased neutrophil to lymphocyte ratio (NLR). For the first time, we investigated NLR variability in mood disorders, a critical aspect of biomarker development. Our study provides a result on the influence of our variables on the NLR and also on the intrinsic properties of the ratio. Consequently, our objective was to analyse the differences in NLR between healthy subjects and patients diagnosed with mood disorder with suicidal behaviour or mood disorder without suicidal attempt. A prospective study was conducted on 97 healthy subjects, 63 patients with mood disorder without suicidal behaviour and 61 patients with mood disorder with suicidal behaviour (mean age [SD] = 44.2 [14.31]; 66.1 % female). Participants were assessed four times over 30 weeks, where blood samples and clinical data were collected. After controlling for confounding factors such as smoking and medical history, we found that NLR stability was low but NLR was significantly associated with a history of suicide attempt (mixed linear model, F = 4.044; p = 0.018). We also observed a significant interaction between NLR values and childhood trauma (p = 0.002). Furthermore, our results demonstrate that NLR is influenced by childhood trauma, including in controls (p = 0.014). Finally, NLR expression differs between patients with and without suicidal behaviour, but only in those without a history of childhood trauma (p = 0.026). Despite its variability over time, our data suggest that NLR may be a promising biomarker for identifying individuals at high risk of suicidal behaviour among patients with mood disorders.