Risk score for identifying adults with CSF pleocytosis and negative CSF Gram stain at low risk for an urgent treatable cause

SummaryBackgroundWe aimed to derive and validate a risk score that identifies adults with cerebrospinal fluid (CSF) pleocytosis and a negative CSF Gram stain at low risk for an urgent treatable cause.MethodsPatients with CSF pleocytosis and a negative CSF Gram stain were stratified into a prospective derivation (n = 193) and a retrospective validation (n = 567) cohort. Clinically related baseline characteristics were grouped into three composite variables, each independently associated with a set of predefined urgent treatable causes. We subsequently derived a risk score classifying patients into low (0 composite variables present) or high (≥1 composite variables present) risk for an urgent treatable cause. The sensitivity of the risk score was determined in the validation cohort and in a prospective case series of 214 adults with CSF-culture proven bacterial meningitis, CSF pleocytosis and a negative Gram stain.FindingsA total of 41 of 193 patients (21%) in the derivation cohort and 71 of 567 (13%) in the validation cohort had an urgent treatable cause. Sensitivity of the dichotomized risk score to detect an urgent treatable cause was 100.0% (95% CI 93.9–100.0%) in the validation cohort and 100.0% (95% CI 97.8–100.0%) in bacterial meningitis patients.InterpretationThe risk score can be used to identify adults with CSF pleocytosis and a negative CSF Gram stain at low risk for an urgent treatable cause.