INTRODUCTION: Neurofilament light chain (NfL) is one of the most important biomarkers in the field of clinical neurochemistry. Several analytical methods have been developed in the last decade. Recently, Fujirebio introduced a ready-to-use assay kit for measuring NfL levels in the cerebrospinal fluid (CSF) on the fully automated LUMIPULSE G System. In this study, we established the decisional cutoffs for CSF NfL. MATERIALS AND METHODS: We performed a retrospective observational study including patients with cognitive decline. CSF NfL levels were measured by two analytical methods: the NF-light ELISA kit (UmanDiagnostics) and the Lumipulse G1200 fully automated system (Fujirebio). We calculated the cutoffs for the Lumipulse, starting from the consolidated cutoffs of the ELISA method for each age and using the equation obtained by the regression analysis. RESULTS: The study population consisted of 100 patients with cognitive decline. The median levels of CSF NfL measured by Lumipulse and ELISA were 776.5 ± 772.6 pg/mL and 473.5 ± 443.5 pg/mL, respectively, significantly different (p <
0.001). The Spearman's rank correlation coefficient was 0.962, indicating a robust positive correlation between the two measurement methods. The equation derived from the Passing-Bablok regression analysis was CSF CLEIA = -61.16 + 1.83 × CSF ELISA. Based on this equation, we defined the decisional cutoff values. CONCLUSIONS: Decisional cutoffs are fundamental tools for guiding clinicians to use biomarkers' results and interpretation appropriately. This is the first study establishing the decisional cutoff value of NfL measured by Lumipulse, a fully automated platform widely used in clinical laboratories.