PT - JOURNAL ARTICLE AU - Gemma Winzor AU - Sowsan F Atabani TI - How and when to use CSF to investigate neonates and children with possible central nervous system infection AID - 10.1136/archdischild-2020-321242 DP - 2021 Mar 19 TA - Archives of disease in childhood - Education & practice edition PG - edpract-2020-321242 4099 - http://ep.bmj.com/content/early/2021/03/18/archdischild-2020-321242.short 4100 - http://ep.bmj.com/content/early/2021/03/18/archdischild-2020-321242.full AB - A child presented to the emergency department with fever, reduced consciousness, irritability and reduced oral intake. Infective meningitis and encephalitis were within the differential diagnoses. Is a lumbar puncture (LP) indicated and, if so, what is the optimal timing of LP? Will antimicrobial pretreatment affect the cerebrospinal fluid (CSF) results? How can clinicians optimise diagnostic stewardship to benefit individual patients and society at large? Interpretation of rapidly available CSF biochemical tests (protein, glucose and lactate levels) and microscopy can provide a prompt insight into the infective aetiology and inform treatment and further diagnostic testing strategies. Diagnosis of an aetiological pathogen in a patient presenting with central nervous system (CNS) infection has clinical, infection control and public health implications. A plethora of tests are available to enable CSF analysis in patients with possible CNS infection. We aimed to summarise current evidence and guidance to ensure the best possible use of the diagnostics available.