Combined Lactate Glucose Ratio (CLGR) as a novel marker for rapid diagnosis of CSF bacterial infection in neurosurgical patients: diagnostic accuracy study and benchtop analyzer correlation.

OBJECTIVE This study aimed to assess the diagnostic accuracy of a novel marker, the combined lactate-to-glucose ratio (CLGR), in identifying cerebrospinal fluid (CSF) bacterial infection (CBI) in neurosurgical patients. Additionally, it seeks to establish cut-off values for CLGR and evaluate the reliability of measurement using blood gas analyzer (BGA). METHODS CSF samples were collected from two neurosurgical centers in Kuala Lumpur, Malaysia, between January 2022 and October 2023. Conventional markers and CLGR were quantified using standard laboratory methods, with BGA utilized for measurement when feasible. Samples were categorized into confirmed CBI-positive (CBI+) and CBI-negative (CBI-) groups. Marker performance was compared, and receiver operating characteristic analysis conducted. Pearson's correlation assessed the agreement between BGA and laboratory measurements. RESULTS Among the 130 CSF samples, 11 were CBI+. Both cLac and CLGR were significantly elevated in the CBI+ group (p<0.001). The area under the curve (AUC) for cLac and CLGR was 0.990 and 0.994, respectively. Using a cut-off of 6.0mmol/L, cLac demonstrated sensitivity of 100%, specificity of 93.3%, positive predictive value (PPV) of 57.9%, negative predictive value (NPV) of 100%, and diagnostic accuracy of 93.9%. CLGR ≥20.0 showed even higher accuracy: 100.0% sensitivity, 98.6% specificity, 84.6% PPV, 100% NPV, and overall accuracy of 98.5%. Both markers maintained excellent performance in blood-stained CSF. BGA measurements correlated well with laboratory results (r=0.980 & 0.999, respectively, p<0.001). CONCLUSIONS CLac levels ≥6.0mmol/L and CLGR ≥20.0 accurately identified CBI in neurosurgical patients, with CLGR exhibiting superior efficacy. The potential for instant BGA measurement suggests promise for point-of-care testing.