CSF to serum glucose ratio in acute bacterial meningitis

Q: What is the usual CSF to serum glucose ratio in acute bacterial meningitis (ABM)?

Answer: ≤0.4

Although conventionally, it is taught that the cerebrospinal fluid (CSF) glucose in ABM should be below 40 mg/dL, a reasonable approach would be to look for CSF to serum glucose ratio, which should be ≤0.4. Other usual findings in ABM are protein >200 mg/dL and Leucocytosis with predominant neutrophils. 

Said that it is not necessary for all findings need to be present in ABM. A clinician's judgment, combined with history and prevalent community epidemiology, plays an essential role.

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References:

1. Tamune H, Takeya H, Suzuki W, Tagashira Y, Kuki T, Honda H, Nakamura M. Cerebrospinal fluid/blood glucose ratio as an indicator for bacterial meningitis. Am J Emerg Med. 2014 Mar;32(3):263-6. doi: 10.1016/j.ajem.2013.11.030. Epub 2013 Nov 26. PMID: 24361137.

2. Powers WJ. Cerebrospinal fluid to serum glucose ratios in diabetes mellitus and bacterial meningitis. Am J Med. 1981 Aug;71(2):217-20. doi: 10.1016/0002-9343(81)90108-x. PMID: 7258216.