The Prevalence of Undiagnosed Concussions and Their Associations With Current Symptom Reporting in Collegiate-Aged Athletes.

Objective: Determine the prevalence of undiagnosed concussions across the lifespan and their association with demographic and injury-related factors, prolonged recovery, and risk for subsequent injury. Test the hypothesis that prior diagnosed and undiagnosed concussions are associated with worse current-day concussion-related symptoms.

Setting: Academic medical center.

Participants: Healthy collegiate-aged athletes with varying levels of prior concussion (N = 212, age 21.00 ±1.69 years, 63% male; N = 125, age 21.05 ±1.67 years, 66% male) with at least 1 prior concussion.

Design: In this cross-sectional single-visit study, semi-structured interviews were used to retrospectively collect concussion history across the lifespan, including whether concussion was diagnosed at time of injury. Generalized linear models determined association of injury-related and demographic factors with diagnosis status at time of injury. Multiple linear regression determined associations of number of diagnosed and undiagnosed concussions with current concussion-related symptom severity.

Main measures: Diagnosis status, days until and number of subsequent concussions, number of days with symptoms for retrospectively identified concussions; Sport Concussion Assessment Tool symptom severity.

Results: Fifty-three percent of the 308 concussions retrospectively identified were not diagnosed as concussion at time of injury. Older age (P = .045, OR = 1.08), greater number of endorsed symptoms (P <. 001, OR = 1.22), presence of post-traumatic amnesia (P = .011, OR = 2.47), and presence of retrograde amnesia (P = .012, OR = 3.19) at the time of injury increased odds of that injury being diagnosed as concussion. Injuries diagnosed as concussion at time of injury were associated with greater number of days with symptoms (B = 11.26(2.01), P < .001). A greater number of diagnosed concussions (B(SE) = 0.19 (0.06), P = .003), and to a lesser extent undiagnosed concussions (B(SE) = 0.11(.06), P = .08), were associated with current symptom severity.

Conclusions: Most concussions experienced by collegiate-aged athletes throughout their life go undiagnosed. Findings do not support the hypothesis that undiagnosed concussions are associated with worse chronic symptom reporting relative to diagnosed concussions but illustrate the need to consider both when characterizing potential long-term effects.