Neutrophil to lymphocyte ratio, platelet to lymphocyte ratio, and monocyte to lymphocyte ratio in depression: A meta-analysis.

Background: The possible associations between depression and neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), and monocyte to lymphocyte ratio (MLR) have been evaluated in numerous studies. But the results were still controversial.

Methods: The WEB OF SCIENCE, PUBMED, EMBASE, and COCHRANE LIBRARY databases were searched for eligible studies. Standardized mean difference (SMD) and 95% confidence interval (CI) were used to assess the differences in NLR, PLR, and MLR levels between depressed patients and controls.

Results: Two thousand five hundred and eighty cases and 2664 controls, 1393 cases and 1370 controls, 744 cases and 765 controls were identified in the meta-analyses for NLR, PLR, and MLR, respectively. The pooled analyses showed that depressed subjects had significantly higher levels of NLR than healthy controls (SMD = 0.33, 95% CI = 0.15-0.15, P < 0.001). Sensitivity analysis and publication bias test confirmed the result. Subgroup analyses suggested that the association between depression and NLR could be affected by country, study design, and antidepressant treatment. While no significant difference of PLR (SMD = 0.13, 95% CI = -0.04-0.31, P = 0.140) and MLR (SMD = 0.02, 95% CI = -0.24-0.28, P = 0.892) values was found between depressed subjects and controls.

Limitations: High heterogeneity was noted across studies.

Conclusions: The present meta-analysis supported the hypothesis that depression is associated with inflammation, and NLR can be used as an indicator of depression. Further large-scale studies are warranted, especially those that evaluate PLR or MLR in depression.