Neutrophil–lymphocyte ratio across psychiatric diagnoses: a cross-sectional study using electronic health records

OBJECTIVES: The main objective of this study was to compare neutrophil–lymphocyte ratio (NLR), a marker of systemic inflammation, between patients diagnosed with International Classification of Diseases 10th Revision (ICD-10) psychiatric disorders and control participants. DESIGN: A cross-sectional methodology was employed to retrospectively analyse electronic health records and records derived from a national health survey. SETTING: A secondary mental healthcare service consisting of four boroughs in South London. PARTICIPANTS: A diverse sample of 13 888 psychiatric patients extracted from South London and Maudsley electronic health records database and 3920 control participants extracted from National Health and Nutrition Survey (2015–2016) were included in the study. PRIMARY AND SECONDARY OUTCOME MEASURES: Primary: NLR levels in patients with mental health diagnoses, NLR between patients with different mental health diagnoses. Secondary: relationship of NLR to length of hospitalisation and to mortality. RESULTS: NLR was elevated compared with controls in patients with diagnoses including dementia, alcohol dependence, schizophrenia, bipolar affective disorder, depression, non-phobic anxiety disorders and mild mental retardation (p<0.05). NLR also correlated with age, antipsychotic use and hypnotic use. NLR was found to be higher in individuals of ‘white’ ethnicity and lower in individuals of ‘black’ ethnicity. Elevated NLR was associated with increased mortality (β=0.103, p=2.9e−08) but not with hospital admissions or face-to-face contacts. CONCLUSIONS: Elevated NLR may reflect a transdiagnostic pathological process occurring in a subpopulation of psychiatric patients. NLR may be useful to identify and stratify patients who could benefit from adjunctive anti-inflammatory treatment.