NEFL and Parkinson disease: Because serum NFL was higher in patients with PD than in patients with ET (p < 0.01, Fig. 1A), the serum NFL cutoff value of 13.65 pg/ml had a 76.7% sensitivity and a 84.1% specificity for distinguishing between PD and ET, with an area under the curve of 0.854 (Fig. 1C).