An elevated neutrophil-to-lymphocyte ratio (NLR) is linked to a higher risk of depressive disorder (DD) and may also be associated with suicide risk in people with DD, according to a systematic review and meta-analysis published in the November issue of Harvard Review of Psychiatry.
"Studies demonstrate altered immune responses in DD, including diminished lymphocyte reactivity and dysregulated neutrophil activity," said Yongjun Chen, MD, of Shandong University of Traditional Chinese Medicine in Jinan, China, and colleagues. "NLR, derived from a routine complete blood count, has emerged as a cost-effective and accessible peripheral biomarker of systemic inflammation." The research team noted that their work is the first comprehensive meta-analysis to examine both predictive and prognostic implications of NLR in patients with DD.
The study involved a search across several databases including PubMed, Embase, the Cochrane Library, and Web of Science up to September 4, 2024. Eligible studies included those involving patients with primary or secondary depression (any subtype) that reported original data on the relationship between DD and NLR with adequate methodological detail.
A total of 37 studies were included in the analysis. These studies were published between 2015 and 2024 and involved 88,019 participants. Of these studies, three provided only categorical NLR data, 27 provided only continuous NLR data, and seven provided both types. Most studies originated from Asia (27), followed by Europe (seven) and the Americas (three). The research designs included six cohort studies and 31 case–control studies. Participants ranged from ages 13 to 83 years old, with sample sizes ranging from 32 to over 34,000.
Study quality was evaluated using the Newcastle–Ottawa Scale in three domains: participant selection, comparability of groups, and outcome ascertainment. All included studies received scores of seven or eight out of nine possible stars.
The researchers performed separate analyses for categorical and continuous variables related to NLR. Sensitivity analysis showed that no single study unduly influenced the overall results.
"These findings underscore the clinical relevance of systemic inflammation in DD pathophysiology," Dr. Chen's group stated. "and highlight NLR as a cost-effective, accessible tool to inform risk stratification and tailored treatment strategies in psychiatric care."
