Neutrophil-lymphocyte ratios as inflammatory biomarkers in psychiatric patients

There is a growing amount of evidence to suggest that inflammation may have a role in the onset and prognosis of psychiatric disorders. We reviewed the literature of studies investigating neutrophil–lymphocyte ratios (NLR), a biomarker of inflammation, in both adult and youth psychiatric populations. The limitations of NLR, in addition to the potential mechanisms underlying its relationship with psychiatric disorders, are also discussed. Unlike in the general population, NLR is elevated in a proportion of adult patients with schizophrenia, major depressive disorder and bipolar disorder, though associations with symptom severity and other clinical parameters are less clear. When compared to baseline, reductions in NLR are sometimes reported after treatment and remission. Results in youth populations largely resemble findings obtained from adult samples, even though youth studies are far fewer in number. The consistent findings of elevated NLR across the reviewed psychiatric disorders suggest that abnormal NLR is not specific to any one disorder but may reflect a pathological brain process that leads to brain dysfunction. These findings support hypotheses of neuroinflammation being important to the etiology of psychiatric disorders. More research is needed to further elucidate the relationship between specific diagnostic and behavioural constructs and NLR. Future work is also needed to determine the specific neuroinflammatory mechanisms that give rise to specific disorders.