Plasma NfL. Findings from linear models (adjusted by age and sex) showed that differences in plasma NfL levels were seen between cognitively unimpaired (CU) and cognitively impaired (CI) subjects in both ADNI (A) and TRIAD (B) cohorts cross-sectionally. Cognitively impaired participants also showed higher plasma NfL concentrations compared to cognitively unimpaired participants (C) longitudinally, as shown by LME modelling.