Age-specific application of neutrophil-to-lymphocyte ratio in meningitis: a nationwide study.

Cerebrospinal fluid (CSF) neutrophil counts and neutrophil-to-lymphocyte ratio (NLR) are useful in distinguishing bacterial and viral meningitis. Given that meningitis is clinically heterogeneous with regard to age, here we investigated the validity of the CSF NLR and neutrophil assay according to age group. Data from the nationwide referral of >4,000 meningitis cases to the Hellenic Meningitis Reference Laboratory between 2006 and 2013 were examined. CSF NLR and neutrophil counts were stratified according to age, and assay performance was determined using previous cut-off values of 2 and 287 cells/μl for CSF NLR and neutrophils respectively. The distribution of bacterial versus viral meningitis was heterogenous across age groups, with a low proportion of bacterial meningitis in patients aged 5-14. CSF neutrophil count and NLR were significantly more discriminatory for bacterial meningitis in patients aged over 14 years than those aged 0-14. The odds ratio (OR), sensitivity, specificity and positive predictive value (PPV) were significantly higher in older patients for both biomarkers. When combined, the false-positive and false-negative detection of bacterial meningitis was 3.9 and 8.5% respectively, and the OR of 262.2 was 2.5-fold greater than expected from a multiplicative effect alone in patients aged >14 years. Care is required when applying diagnostic tests for meningitis in different age groups because of patient heterogeneity. This is the first description of the age distribution of meningitis cases in Greece, and knowledge of the age-related distribution of neutrophils and NLR in meningitis cases could help towards developing age-specific meningitis diagnostic assays.