Following the lactate trail: sequential CSF lactate trend analysis in diagnosing post-neurosurgical meningitis – a single‑center experience

Objectives Post-neurosurgical bacterial meningitis (PNBM) is one of the major complications that causes high mortality in an era of antimicrobial resistance. Differentiating infective meningitis from aseptic meningitis remains challenging when we rely on culture, as it has lower sensitivity, and conventional cerebrospinal fluid biomarkers cannot differentiate between the two.Methods This study aimed to evaluate the diagnostic utility of sequential cerebrospinal fluid lactate as a biomarker in patients with PNBM, to establish the optimal cutoff. This retrospective study included 49 PNBM and 27 non-PNBM patients from January to December 2024. In each category, a minimum of 3 and a maximum of 5 samples were considered for sequential CSF lactate analysis. In the PNBM group, ROC curve analysis revealed that CSF lactate levels had the highest diagnostic accuracy (AUC of 0.89, Youden’s index, 0.78), followed by cell count (AUC of 0.86), glucose (AUC of 0.79), and protein (AUC of 0.49).Results Sequential CSF lactate analysis showed a significant difference between the PNBM and non-PNBM groups (p < 0.001). The optimal CSF lactate cutoff was 4.7 mmol/L, with 90% and 89% sensitivity and specificity, respectively. Among non-survivors, the average CSF lactate was 6.1 mmol/L compared to that of survivors.Discussion Our study shows that rather than relying on a single value, sequential CSF lactate monitoring helps to identify meningitis cases earlier than other CSF biomarkers and when culture results remain negative. A CSF lactate of 4.7 mmol/L serves as a diagnostic marker for PNBM, with >6.1 mmol/L being associated with higher mortality.