A systematic review for the World Health Organization quantified how well common CSF parameters distinguish bacterial meningitis, using 27 studies and 5,673 patients with suspected acute meningitis. The meta-analysis found Gram stain specificity was high at 99%, but sensitivity was variable and pathogen-dependent. Gram stain sensitivity reached 85% overall, yet fell to 10–25% for Listeria monocytogenes—meaning many Listeria cases could be missed by reliance on Gram stain alone. Lactate emerged as the strongest single test in the analysis, with 94% sensitivity and 86% specificity, while other markers showed more moderate and less consistent performance. The results feed directly into guideline development and underscore how diagnostic algorithms must incorporate both test characteristics and expected pathogen distributions. For clinicians, the takeaway is operational: a negative Gram stain should not reliably rule out bacterial meningitis, particularly for Listeria.