Serum Neurofilament Light Chain and GFAP in Amyotrophic Lateral Sclerosis on a Commercial ECLIA Platform.

INTRODUCTION/AIMS: In amyotrophic lateral sclerosis (ALS), SIMOA-based studies show that baseline serum neurofilament light chain (NfL) predicts the revised ALS Functional Rating Scale (ALSFRS-R) decline rate and survival. The Roche Elecsys electrochemiluminescence immunoassay (ECLIA) reports values approximately six-fold lower; cross-platform comparison confirms comparable performance, but serial clinical-practice data remain limited. We assessed whether ECLIA NfL correlates with the ALSFRS-R decline rate under the sampling conditions of clinical practice, and whether GFAP or S-100B adds prognostic or disease-specific information. METHODS: We retrospectively analyzed 58 patients with medical-record-confirmed ALS at an academic center (2022-2026). Serum NfL, GFAP, and S-100B were measured on the Roche Elecsys ECLIA. The NfL-ALSFRS-R correlation was assessed within matching windows; serial NfL was examined in patients with repeat draws. RESULTS: First-per-patient NfL median was 7.06 pg/mL (IQR 4.06-17.30). NfL correlated strongly with the ALSFRS-R decline rate (Spearman r = 0.704, n = 31; r = 0.809 within 90 days, n = 17; both p < 0.0001). Fast progressors had 3.7-fold higher mean NfL than slow progressors (17.10 vs. 4.64 pg/mL). NfL showed no correlation with King's clinical stage (r = 0.00). GFAP correlated with age but not with progression rate or disease duration; S-100B showed no association with progression. DISCUSSION: Serum NfL on a commercial ECLIA platform retained its strong correlation with progression rate despite unstructured sampling, replicating SIMOA-based findings at platform-specific values. NfL tracked the rate of decline rather than the accumulated disease state; GFAP and S-100B added no prognostic or disease-specific information.