Optimization of cutoff values for (1→3)-β-<scp>d</scp>-glucan and galactomannan assays in cerebrospinal fluid for the diagnosis of non-cryptococcal fungal infections of the central nervous system

Fungal infections of the central nervous system (FI-CNS) pose substantial diagnostic challenges, owing to their diverse clinical presentations and the limited sensitivity of conventional diagnostic tests. Although serum (1→3)-β-d-glucan (BDG) and galactomannan (GM) assays are FDA-approved for the diagnosis of invasive fungal infections (IFIs), their effectiveness in cerebrospinal fluid (CSF) remains underexplored, and optimal cutoff values in CSF are not well established. This study aimed to assess the utility of BDG and GM assays in CSF for diagnosing non-cryptococcal FI-CNS. We conducted a prospective observational study at the National Institute of Mental Health and Neuro Sciences in India from January 2022 to December 2023, including CSF samples from patients suspected of fungal meningitis. The cases were categorized as proven, probable, or possible FI-CNS based on the revised EORTC/MSGERC criteria. Among 61 suspected cases, 2 were proven, 48 were probable, and 11 were possible FI-CNS. The control group included 23 patients without FI-CNS suspicion. BDG and GM testing in CSF followed manufacturers' guidelines for serum. At the manufacturer's recommended cutoff of 80 pg/ml, sensitivity of BDG was 94% and specificity was 78.3%. For GM, using the manufacturer's recommended cutoff of 0.5 optical density index (ODI), sensitivity was 42% and specificity was 100%. Receiver operating characteristic curve analysis indicated optimal cutoffs of 72 pg/ml for BDG (sensitivity 96%, specificity 78.3%) and 0.47 ODI for GM (sensitivity 44%, specificity 100%). Combining both biomarkers increased sensitivity to 97.8%, suggesting that combined BDG and GM testing in CSF could significantly enhance the diagnostic accuracy and management of FI-CNS.