Serum neurofilament light as a biomarker for mild traumatic brain injury in contact sports.

OBJECTIVE To evaluate whether the axonal protein neurofilament light (NFL) in serum is a sensitive biomarker to detect subtle brain injury or concussion in contact sports athletes. METHODS Two prospective cohort studies involving (1) 14 Swedish amateur boxers who underwent fluid biomarker assessments at 7-10 days after bout and after 3 months of rest from boxing and (2) 35 Swedish professional hockey players who underwent blood biomarker assessment at 1, 12, 36, and 144 hours after concussion and when the players returned to play were performed. Fourteen healthy nonathletic controls and 12 athletic controls were also enrolled. Serum NFL was measured using ultrasensitive single molecule array technology. RESULTS Serum NFL concentrations were increased in boxers 7-10 days after bout as compared to the levels after 3 months rest as well as compared with controls (p = 0.0007 and p < 0.0001, respectively). NFL decreased following 3 months of rest, but was still higher than in controls (p < 0.0001). Boxers who received many (>15) hits to the head or were groggy after bout had higher concentrations of serum NFL as compared to those who received fewer hits to the head (p = 0.0023). Serum NFL increased over time in hockey players, and the levels returned to normal at return to play. Importantly, serum NFL could separate players with rapidly resolving postconcussion symptoms (PCS) from those with prolonged PCS. CONCLUSIONS The results from these 2 independent cohort studies suggest that serum NFL is a highly sensitive biomarker for concussion.