Value of cerebrospinal fluid lactate for the diagnosis of bacterial meningitis in postoperative neurosurgical patients.

OBJECTIVE To evaluate the diagnostic value of CSF lactate (L(CSF)) for the diagnosis of bacterial meningitis (BM) following neurosurgery, and compare it with other CSF markers. METHODS Prospective study of consecutive neurosurgical postoperative patients admitted to the Intensive Care Unit (ICU) at Maciel Hospital. Patients with clinical suspicion of BM were categorised, according to preset criteria, into 3 groups: (1) proven BM; (2) probable BM, and (3) excluded BM. CSF markers were plotted in a receiver operating curve (ROC) to evaluate their diagnostic accuracy. RESULTS The study included 158 patients. We obtained 46 CSF samples from patients with clinical suspicion of BM by lumbar puncture (LP): 10 corresponded to proven BM, 4 to probable BM and 32 to excluded BM. Mean lactate in CSF (L(CSF)) was: 10.72±4.68mM for proven BM, 6.07±0.66mM for probable BM and 3.06±1.11mM for excluded BM (P<.001 for proven BM and probable BM vs excluded BM; P=NS for proven BM vs probable BM). L(CSF) displayed a better diagnostic accuracy for BM in the 2 scenarios studied: (1) positive bacterial CSF culture or Gram stain as positive control (gold standard) (sensitivity: 87%, specificity: 94%, cut-off value: 5.9mM), and (2) combination of proven BM and probable BM as positive control (sensitivity: 92%, specificity: 100%, cut-off value: 5.2mM). CONCLUSIONS According to our results, determination of L(CSF) is a quick, sensitive and specific test to identify the need for antimicrobial therapy in neurosurgical postoperative patients with clinical suspicion of BM.