Clinical question: What is the association between cerebrospinal fluid (CSF) red blood cell (RBC) counts and protein concentrations in infants younger than 57 days of age?
Background: Lumbar puncture (LP) is commonly performed in young infants to evaluate for meningitis in the clinical scenario of fever without source. Traumatic LP is common in children, and higher RBC counts are associated with increased CSF protein concentrations. The dynamic nature of CSF composition in young infants makes determination of the exact relationship between RBC counts and protein concentration challenging, which then complicates interpretation of CSF.
Study design: Retrospective, cross-sectional study.
Setting: Tertiary-care children's hospital.
Synopsis: Over a four-year period, 1,241 infants younger than 57 days of age that underwent LP were studied, excluding infants with conditions known to increase CSF protein concentrations: ventricular shunt, serious bacterial infection, congenital infection, herpes simplex virus or enterovirus positive PCR in CSF, seizure, or elevated serum bilirubin. Grossly bloody specimens with RBC counts >150,000 cells/mm3 were also excluded. Linear regression was used to determine relationship between CSF RBCs and protein, with protein increasing at a rate of 1.9 mg/dL per 1,000 CSF RBCs.
This ratio is different from a more traditional correction factor of approximately 1 mg/dL CSF protein increase per 1,000 CSF RBCs, which is derived from older populations of children.
However, this study is limited by the exclusion of grossly bloody specimens, which if included would have resulted in a ratio similar to the more traditional values. Additionally, application of this specific correction factor to prediction rules for bacterial meningitis has not been studied. Nonetheless, this study provides a baseline by which clinicians may interpret protein concentrations in traumatically bloody CSF specimens in young infants.
Bottom line: CSF protein concentrations increase at roughly 2 mg/dL per 1,000 CSF RBCs.
Citation: Hines BA, Nigrovic LE, Neuman MI, Shah SS. Adjustment of cerebrospinal fluid protein for red blood cells in neonates and young infants. J Hosp Med. 2012;7:325-328.
Reviewed by Pediatric Editor Mark Shen, MD, SFHM, medical director of hospital medicine at Dell Children's Medical Center, Austin, Texas.