CSF Tests for Bacterial Meningitis: What a Major Meta-Analysis Found

When doctors suspect bacterial meningitis, they depend on cerebrospinal fluid (CSF) analysis to confirm or rule out the disease quickly, because delays in treatment can be fatal. A new systematic review and meta-analysis, carried out to inform the World Health Organization’s guidelines for diagnosis, treatment and care, has now quantified how well the most commonly used CSF parameters actually perform in distinguishing bacterial meningitis from other conditions.

The analysis, published in BMC Medicine, pooled data from 27 studies covering 5,673 patients with suspected acute meningitis. The researchers, led by Nina S. Groeneveld and Matthijs C. Brouwer, evaluated the diagnostic accuracy of Gram stain, leukocyte count and differential, glucose, total protein, and lactate, reporting sensitivity, specificity, positive and negative predictive values, likelihood ratios, and the area under the receiver operating characteristics curve.

Across all included studies, the overall sensitivity of the Gram stain was 85 percent, with a 95 percent confidence interval of 55 to 96 percent, while its specificity reached 99 percent. In other words, when the stain shows bacteria, the result is almost always correct, but a negative stain does not reliably exclude infection.

Strikingly, the sensitivity of the Gram stain varied enormously depending on the pathogen involved. For Neisseria meningitidis, it ranged from 30 to 89 percent, and for Haemophilus influenzae from 25 to 65 percent. Most concerning was Listeria monocytogenes, for which the Gram stain detected only 10 to 25 percent of cases, meaning the test misses most infections with this organism.

The other CSF parameters showed a more consistent but generally more moderate profile. The CSF leukocyte count had a sensitivity of 77 percent and a specificity of 83 percent, while the neutrophil count performed slightly better, with 82 percent sensitivity and 84 percent specificity. CSF glucose was less sensitive, at 66 percent, but highly specific at 85 percent, and the CSF to blood glucose ratio showed 88 percent sensitivity with 78 percent specificity.

Two parameters stood out for their combined performance. CSF total protein achieved a sensitivity of 86 percent and a specificity of 79 percent, while CSF lactate was the strongest single test in the analysis, with 94 percent sensitivity and 86 percent specificity. These figures suggest that an elevated lactate level, together with raised protein and a neutrophil-predominant pleocytosis, provides the strongest statistical signal of bacterial meningitis among the routinely available CSF measurements.

The authors conclude that an elevated CSF leukocyte count, specifically neutrophils, along with CSF protein concentration and CSF lactate, are predictive of bacterial meningitis, and that a decreased CSF glucose concentration and a low CSF to blood glucose ratio are also predictive. At the same time, they emphasize that the Gram stain’s high specificity comes with sensitivity that varies by pathogen and is only moderate for several important organisms, a limitation with direct consequences for how clinicians should interpret a negative stain.

The meta-analysis also highlights what remains unknown. The authors state that further studies are needed to assess combinations of these tests and novel biomarkers to improve diagnostic accuracy.

As the WHO develops its guidelines for meningitis diagnosis, treatment and care, this synthesis of 27 studies and nearly 5,700 patients provides the quantitative foundation for deciding which CSF parameters deserve a central place in that guidance.

Subject of Research: Diagnostic accuracy of cerebrospinal fluid parameters for bacterial meningitis

Article Title: Diagnostic performance of cerebrospinal fluid examination in cases with suspected acute meningitis: a systematic review and meta-analysis

Article References: Groeneveld, N. S., Olie, S. E., Binello, N., Kothari, K., Venuti, F., Movsisyan, A., Dua, T., Schiess, N., & Brouwer, M. C. (2026). Diagnostic performance of cerebrospinal fluid examination in cases with suspected acute meningitis: a systematic review and meta-analysis. BMC Medicine. https://doi.org/10.1186/s12916-026-05302-z

Image Credits: AI Generated

DOI: 10.1186/s12916-026-05302-z

Keywords: bacterial meningitis, cerebrospinal fluid, Gram stain, diagnostic accuracy, meta-analysis, CSF lactate, CSF protein, leukocyte count, WHO guidelines, Listeria monocytogenes, Streptococcus pneumoniae, BMC Medicine