NEFL and concussion: Compared with controls, blood UCH-L1 and tau levels are typically higher among recreational athletes, even in the absence of a TBI or concussion.28,29 Serum NfL level has been reported to be a prognostic factor associated with negative outcomes after diagnosed TBI.30,31 Overall, the concentration range of UCH-L1, tau, or NfL may be higher in military and law enforcement personnel even at rest owing to physical training.