Which CSF finding is characteristic of bacterial meningitis?

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In bacterial meningitis, cerebrospinal fluid (CSF) analysis reveals a characteristic profile that includes a predominance of polymorphonuclear leukocytes (PMNs) and low glucose levels. This reflects the acute inflammatory response to bacterial infection, as bacteria induce a robust immune response that leads to the recruitment of PMNs to the site of infection.

Low glucose levels in CSF occur because bacteria metabolize glucose and there is increased consumption by white blood cells during the inflammatory response. Typically, CSF glucose levels in cases of bacterial meningitis are significantly lower compared to serum levels, often dropping to less than 40% of the serum glucose value.

The combination of low glucose and a high PMN count is a key diagnostic feature that can help differentiate bacterial meningitis from other types, such as viral meningitis, where lymphocytic predominance and normal glucose levels are more common.

Other findings, such as increased gamma globulins, might suggest chronic inflammatory processes, but they are not characteristic of acute bacterial infections. Similarly, numerous red blood cells would suggest bleeding or a traumatic tap rather than an infection. Hence, the combination of low glucose and PMN predominance is specific to bacterial meningitis, confirming the diagnosis.

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