NEFL and amyotrophic lateral sclerosis: However, we found a significant positive correlation between serum NfL levels and cystatin C among ALS (Pearson’s p = 0.018, Spearman’s rank p = 0.143) and among HC (Pearson’s p = 0.004, Spearman’s rank p = 0.491) and a significant negative correlation of the corresponding eGFR (Pearson’s p = 0.037, Spearman’s rank p = 0.132) in ALS, but not in HC (Pearson’s p = 0.098, Spearman’s rank p = 0.534).