The King–Devick test was useful in management of concussion in amateur rugby union and rugby league in New Zealand

• The King–Devick (K–D) test was used for routine sideline concussion assessment.
• The K–D had an overall ICC of 0.92 (0.88 to 0.94) over three years.
• The K–D had an overall sensitivity of 1.00, specificity or 0.94 and kappa of 0.98.
• The K–D and SCAT3 helped identify cognitive impairment in players without symptoms.
• There was a significant correlation between the K–D and the SAC total scores.

AimTo use the King–Devick (K–D) test in senior amateur rugby union and rugby league players over a domestic competition season to see if it could identify witnessed and unwitnessed episodes of concussion that occurred from participation in competition matches over three years.MethodsA prospective observational cohort study was conducted on a club level senior amateur rugby union team (n = 36 players in 2012 and 35 players in 2013) and a rugby league team (n = 33 players in 2014) during competition seasons in New Zealand. All 104 players completed two trials 10 min apart of the K–D at the beginning of their competition season. Concussions (witnessed or unwitnessed) were only recorded if they were formally diagnosed by a health practitioner.ResultsA total of 52 (8 witnessed; 44 unwitnessed) concussive events were identified over the duration of the study resulting in a concussion injury incidence of 44 (95% CI: 32 to 56) per 1000 match participation hours. There was a six-fold difference between witnessed and unwitnessed concussions recorded. There were observable learning effects observed between the first and the second K–D test baseline testing (50 vs. 45 s; z = − 8.81; p < 0.001). For every 1 point reduction in each of the post-injury SAC components there was a corresponding increase (worsening) of K–D test times post-match for changes in orientation (2.9 s), immediate memory (1.8 s) concentration (2.8 s), delayed recall (2.0 s) and SAC total score (1.7 s).DiscussionThe rate of undetected concussion was higher than detected concussions by using the K–D test routinely following matches. Worsening of the K–D test post-match was associated with reduction in components of the SAC. The appeal of the K–D test is in the rapid, easy manner of its administration and the reliable, objective results it provides to the administrator. The K–D test helped identify cognitive impairment in players without clinically observable symptoms.