NEFL and Parkinson disease: Under refrigerated centrifugation, early PD demonstrated significantly higher levels of NFL (15.23 ± 9.59 pg/ml) compared with HCs (9.84 ± 4.81 pg/ml, P = 0.028, Figure 6D), but not significantly different between advanced PD (12.22 ± 6.1 pg/ml) and HCs (9.84 ± 4.81 pg/ml, P = 0.669).