Therefore, in this study, the Simoa technology is used to: determine the serum NFL levels in Chinese ALS patients and healthy controls (HCs); and to examine the clinical relevance of the serum NFL in Chinese ALS patients involving the association between the serum NFL level and indicators of disease severity (evaluated using the ALSFRS-r score and disease stage) and progression (evaluated using DPR and diagnostic delay). Here, NEFL is linked to amyotrophic lateral sclerosis.