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Contributor: Eric Miller, MD Educational Pearls: A cell count is performed on tubes 1 and 4 to account for changes that may occur from blood entering the first sample from the needle insertion Tube 2 and 3 are usually used for the other studies like protein levels, glucose levels and gram staining Protein levels are often elevated in bacterial meningitis but can be helpful in diagnosis conditions like multiple sclerosis Glucose levels are typically low in bacterial meningitis due to the use of glucose by bacteria Cell counts above 3-5 cells are typically abnormal, but cell counts can vary widely depending on the type of meningitis (viral vs. bacterial) and how long the infection has been present. Cell type and differential can indicate viral vs. bacterial meningitis Neutrophils are more associated with bacterial causes Lymphocytes are more associated with viral etiologies CSF cultures are used to identify the cause of bacterial meningitis but can take days to result. A gram stain can help determine if any bacteria are present as well as cell types present. References Jain, R. Chang, WW. Emergency Department Approach to the Patient with Suspected Central Nervous System Infection. Emerg Med Clin North Am. 2018 Nov;36(4):711-722. doi: 10.1016/j.emc.2018.06.004. Summarized by Jackson Roos, MS3 | Edited by Erik Verzemnieks, MD