Haematological markers of inflammation in major depressive disorder (MDD) patients with suicidal behaviour: A systematic review and meta-analysis

Abstract

Introduction: Suicide is a significant global health issue linked to neuroinflammation. This study assessed neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR) as systemic inflammation indicators in suicidal behaviour of major depressive disorder (MDD) patients.

Methods: The search included databases like Scopus, PubMed, PsycINFO, Web of Science, and CINAHL Complete, focusing on English-language observational studies up to March 2025. It examined the NLR, PLR, and MLR in individuals with MDD exhibiting suicidal behaviour, comparing them to MDD patients without such behaviors or healthy controls. Study quality was assessed using the Newcastle-Ottawa Scale (NOS), and data analysis utilized Stata software version 17.

Results: From an initial 131 articles, ten studies were included, analyzing 2017 participants. MDD patients with suicidal behaviour had significantly elevated NLR levels compared to non-suicidal MDD patients (SMD: 0.34 [0.12, 0.56]; I²: 67.68 %) and healthy controls (SMD: 1.02 [0.28, 1.76]; I²: 96.15 %). Additionally, no differences in PLR levels were found in suicidal MDD patients compared to their non-suicidal counterparts (SMD: 0.11 [-0.04, 0.27]; I²: 38.39 %), but PLR levels were higher in comparison to healthy controls (SMD: 0.38 [0.17, 0.59]; I²: 38.02 %). Four studies showed higher MLR levels in suicidal MDD patients compared to the non-suicidal group (SMD: 0.33 [0.04, 0.62]; I²: 71.60 %) and healthy controls (SMD: 0.32 [0.06, 0.59]; I²: 44.37 %).

Conclusion: Increased inflammatory biomarkers in MDD patients with suicidal tendencies highlight the need for further research on their potential as suicide vulnerability indicators and the utility of NLR, PLR and MLR in clinical practice.

Keywords: Depression; Neuroinflammation; Suicidal attempt; Suicidal ideation; Suicide.