Anyone who has done a lumbar puncture (LP) in an infant two months of age or younger is used to getting a few white blood cells (WBCs) reported in the cell count of the cerebrospinal fluid (CSF). What is the threshold for saying there are too many white cells to be considered a normal LP? Thomson et al. (10.1542/peds.2017-3405) tackle this question by performing a multicenter cross-sectional study of over 7700 infants less than 60 days of age with CSF cell counts, protein and glucose levels and cultures. Those who were highly suspected to have meningitis or who stayed in the hospital for more than 3 days were not counted in this study to ascertain what a normal CSF looked like. The authors further separated their findings into those infants < 28 days and those who were 29-60 days of age.
This blog will not go into detail regarding how they established their thresholds for normal versus abnormal but the findings are extremely helpful in defining upper limits of normal for WBC counts (with the upper limit being 15 cells/mm3 in babies less than a month of age and 9 cells/mm3 for those between 1 and 2 months of age; higher ranges of protein for those under a month versus those over a month (127 mg/dL versus 99 mg/dL) and for glucose (with a lower floor of 25g/dL versus 27 mg/dL) were identified. If you have been waiting for an updated set of standards for normal CSF interpretation in our youngest patients, this paper’s findings will serve as an excellent reference tool when you are worried enough about an infant to perform an LP and obtain CSF. You’ll probably want to print out this study and keep the reference levels where they can be easily referred to in your office, emergency room, or hospital setting.