Establishing age-stratified reference values for blood Neurofilament Light chain (NfL) using the Lumipulse® platform

Objectives: Neurofilament light chain (NfL) is a sensitive biomarker of neuroaxonal injury detectable in blood and cerebrospinal fluid. Its concentrations are strongly influenced by age, yet no age-specific reference values have been established for the fully automated Lumipulse® platform, and no direct comparison between serum and plasma has been reported for this assay. Methods: Matched serum and plasma samples from 49 participants were analyzed to assess matrix comparability using correlation, paired comparison, and equivalence testing within predefined ±15% bounds. Reference values were determined in 211 control adults aged 18-87years from two international centers. Age groups were derived using K-means clustering, and multivariable linear regression was applied to examine the effects of recruitment center, age, and sex. Results: Serum and plasma NfL levels were highly correlated (Spearman's ρ=0.969, P<0.001). Although serum values were slightly higher than plasma (+3.07pg/mL, P=0.042), the difference was within equivalence margins (P=0.019), indicating that either matrix can be used without compromising clinical interpretation. NfL concentrations increased markedly with age (Spearman's ρ=0.721, c<0.001), with median values rising from 8.45pg/mL in individuals aged 18-34years to 23.4pg/mL in those aged ≥69years. Reference values were defined as the 97.5th percentile and were 18.0pg/mL for patients aged 18-50, 25.4pg/mL for those aged 51-68, and 43.5pg/mL for patients aged 69years or older. No significant effect of sex was observed after adjusting for age. Conclusions: This is the first study to establish serum-plasma comparability for NfL on the Lumipulse® platform and to provide age-stratified reference values in control adults, emphasizing the need for age-adjusted interpretation when distinguishing pathological elevations from normal age-related changes.