NEFL and Alzheimer disease: Compared to A + CU, plasma NfL levels in A + SCD showed a numeric (Fig. 1B) but statistically non-significant elevation (17.7 ± 1.3 vs 13.7 ± 1.2 pg/mL; p = 0.276), and NfL levels were then further elevated in A + MCI (22.0 ± 1.6 pg/mL) compared to A + SCD (p = 0.008) (for stepwise increase pattern across the three pre-dementia AD stages, see Fig. 1B).