Inflammatory biomarkers are reportedly increased in depressed patients. Several studies have been conducted using neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), and monocyte/lymphocyte ratio (MLR). The objective of this systematic review was to study the relationship between these peripheral biomarkers and suicidality in depressed patients with/without suicidal behavior, including suicide attempts and ideation, and healthy controls.

We searched the following relevant terms in the PubMed, Web of Science, and Scopus databases published in the last 5 years. We assessed the methodological quality of included studies using the Oxford criteria and reviewed the evidence following PRISMA guidelines.

Eleven studies were retained for the data synthesis, with a total sample of 1,701 participants, of which the majority (819) were patients with depression and suicidal behavior, 494 were depressed patients without suicidal behavior, and only 388 were healthy participants. Our results reinforce the idea that NLR could be an attractive, convenient, and cost-effective trait marker of suicidal vulnerability in patients with major depressive disorder (MDD).

Future large-scale replication studies are needed to examine the apparently understudied role of PLR and MLR in depressed patients in greater depth.