The aim of this study was to systematically evaluate the pre-analytical stability of NfL in blood, measured using the Lumipulse® G NfL Blood(CE) assay (Fujirebio Europe N.V.), in serum and K2-EDTA plasma. Analyte stability was assessed under commonly encountered storage and handling conditions, including room temperature, refrigerated and frozen storage, multiple freeze/thaw cycles, and fresh versus frozen comparisons, in order to support robust specimen management recommendations for clinical research and routine laboratory use.