Real-World Serum Neurofilament Light Chain and GFAP in Amyotrophic Lateral Sclerosis on a Commercial ECLIA Platform

Background: Neurofilament light chain (NfL) gained FDA recognition in amyotrophic lateral sclerosis (ALS) through SIMOA-based validation, where baseline serum NfL predicts ALSFRS-R slope and survival, and through the 2023 tofersen approval for SOD1-ALS. The commercial Roche Elecsys electrochemiluminescence immunoassay (ECLIA) reads 6- to 8-fold lower than SIMOA, and its clinical utility in ALS is uncharacterized. We assessed whether ECLIA NfL retains this correlation in routine care and whether GFAP or S-100B helps. Methods: Retrospective analysis of 58 chart-confirmed ALS patients at Georgetown University Hospital (2022-2026), biomarkers on the LabCorp Roche Elecsys ECLIA. The NfL-ALSFRS-R correlation was assessed where both measures fell within matching windows; serial NfL, in patients with repeat draws. Results: First-per-patient NfL median was 7.06 pg/mL (IQR 4.06-17.30; CV 99%). Among 31 patients with matched NfL and ALSFRS-R decline rates, Spearman r = 0.704; within 90 days (n = 17), r = 0.809 (both p < 0.0001). Fast progressors (n = 8) had mean NfL 17.10 pg/mL versus 4.64 in slow progressors (n = 21), a 3.7-fold separation. Serial NfL captured rising trajectories and stable low values. GFAP rose within patients but tracked neither progression rate, disease stage, nor motor-neuron predominance; S-100B added no value. Conclusions: Commercial ECLIA brings NfL into routine ALS care; its prognostic correlation with progression rate survives real-world fragmentation. The actionable unit is the longitudinal trajectory, not the single value, read against platform-specific reference ranges and clinical context (genotype, onset, stage). GFAP and S-100B add little. Keywords: amyotrophic lateral sclerosis, neurofilament light chain, biomarkers, implementation science, ECLIA, GFAP, monitoring, tofersen, real-world data