Adjustment of cerebrospinal fluid protein for red blood cells in neonates and young infants

OBJECTIVE: To determine the relationship between cerebrospinal fluid (CSF) red blood cell (RBC) count and CSF protein in neonates and young infants undergoing lumbar puncture. DESIGN: Cross-sectional study. SETTING: Urban tertiary care children's hospital. PATIENTS: Infants 56 days of age and younger who had a lumbar puncture in the emergency department between January 1, 2005 and July 31, 2009 were eligible for inclusion. Infants with missing laboratory data, exceedingly high CSF red blood cell counts, or conditions known to elevate CSF protein were excluded. MEASUREMENTS: Linear regression was used to determine the association between CSF RBC and CSF protein. RESULTS: Of 1986 infants, 56 days of age or younger, who underwent lumbar puncture in the emergency department during the study period, 1241 (62.5%) met inclusion criteria. The median age was 34 days (interquartile range: 19-46 days); 45% of patients were male. The median CSF RBC count was 40 cells/mm(3) (interquartile range: 2-1080 cells/mm 3); 11.8% of patients had a CSF RBC > 10,000 cells/mm 3. CSF protein increased by 1.9 mg/dL (95% confidence interval: 1.7-2.1 mg/dL) per 1000 CSF RBCs for all included patients. Restricting analysis to patients without pleocytosis yielded comparable results, as did subanalyses by age and delivery type. CONCLUSIONS: We found that CSF protein concentrations increased by approximately 2 mg/dL for every 1000 CSF RBCs. These data may assist clinicians in interpreting CSF protein concentrations in infants 56 days of age and younger in the context of traumatic lumbar punctures. Journal of Hospital Medicine 2012;7:325-328. (C) 2012 Society of Hospital Medicine