Effect of delay in analysis on neonatal cerebrospinal fluid parameters.

OBJECTIVES: The effect of delayed analysis on cerebrospinal fluid (CSF) white blood cell (WBC) count and glucose has never been studied in neonates. DESIGN: Prospective cohort study. SETTING: Level III newborn unit. PATIENTS: Neonates undergoing lumbar puncture were enrolled after consent. CSF was analysed at baseline (30 minutes) for protein, WBC and glucose; and from the same sample for WBC and glucose after a lag of 2 h and 4 h after lumbar puncture. Those with traumatic/inadequate CSF were excluded. Subjects were classified in three groups (n = 20 each) based on baseline WBC count: no WBC, 1-30 WBC and >30 WBC/microl. Analysis was by repeated-measures ANOVA. RESULTS: There was a significant decline in mean (SD) CSF glucose from baseline to 2 h and 4 h (41.0 (19) to 38.3 (19) and 36.2 (20) mg/dl, respectively) and WBC count (36 (45) to 28.6 (38) and 23.8 (34) cells/microl, respectively; both p<0.001). CSF glucose and WBC declined in all three groups (p<0.001). High baseline CSF WBC (p<0.001) and protein (p<0.001) was associated with a more rapid decline in the levels of CSF WBC, but not glucose. True CSF parameters could be predicted from 4-h parameters: "baseline glucose 5.4 + 0.98 (4-h glucose)" (adjusted R(2) 97.2%, p<0.001) and "baseline WBC 1.3 (4-h WBC) +0.05 (protein)" (adjusted R(2) 98.8%, p<0.001). In group 3, a diagnosis of meningitis (based on pleocytosis) would be missed in 52.6% and 78.9% subjects at 2 h and 4 h, respectively. CONCLUSIONS: CSF WBC count and glucose decrease significantly with time. Reliance on WBC counts of delayed samples can result in underdiagnosis.