Objective To investigate the association of acute-phase non-invasive salivary biomarkers with sport-related concussion (SRC) in professional men’s rugby.

Design Prospective cohort study.

Setting England’s Premiership and Championship rugby clubs.

Participants Twenty-two out of twenty-four clubs participated across 2 seasons (2017/18 and 2018/19). 1028 subjects were recruited, of whom 391 went on to be included as either concussed or matched controls under the World Rugby Head Injury Assessment protocol (HIA).

Interventions Saliva was obtained from athletes during pre-season and during HIA evaluations during matches and up to 48 hours later. Samples were also collected from matched uninjured players and musculoskeletal controls from the same game.

Outcome Measures T-test and principal component analysis were used to identify small non-coding RNAs (sncRNAs) differentially expressed across groups in a prespecified analysis. A predictive logistic regression model was built on 2017/18 data (training-dataset) and prospectively validated in the 2018/19 season (test-dataset).

Main Results 36 salivary sncRNAs could reliably differentiate concussion from control groups and baselines with AUCs ranging from 0.61 to 0.89. On logistic regression, a panel of 14 sncRNAs could differentiate concussed subjects from controls immediately after the match (AUC 0.91, 95%-CI 0.81–1) and 36–48 hours later (AUC 0.94, 95%-CI 0.86–1). When prospectively tested on new independent data from season-2, the same panel showed high predictive accuracy across all groups and time points (AUC 0.96, 95%-CI 0.92–1 post-match and AUC 0.93, 95%-CI 0.86–1 at 36–48 hours).

Conclusion This large prospective observational study has identified and characterised unique diagnostic signatures of SRC in saliva for the first time, which can aid clinical decision-making in sport, as well as healthcare and defence medicine.