A new study conducted by researchers at the University of Birmingham in the U. K. has found that biomarkers in saliva may be useful for diagnosing a concussion. Concussions can currently only be diagnosed based on symptoms and clinical evaluation, and it is common for athletes to hide their symptoms so they can continue to play. An objective test that could quickly and easily diagnose concussions would be a game changer. This has been covered widely in the media, with some headlines reading “New Saliva Test Can Quickly Diagnose Concussions.” But are the headlines accurate? What does this mean for athletes playing sports today?
What did the study find?
The study was conducted in male professional rugby players in England across two seasons of play. All athletes gave saliva samples before the season started as a baseline. Then those who were assessed for a head injury in a game provided saliva samples during the in-game evaluation, immediately after the game, and 36 to 48 hours post-game. Uninjured players who played in the same game and players who were removed from the game due to a musculoskeletal injury also provided saliva samples at the post-game time points.
This study design allowed for a comparison to each athlete’s own baseline sample as well as between concussed athletes, those who were assessed but determined not to have a concussion, and other athletes who played in the game. That is an important strength of the study. Repetitive head impacts have been shown to cause changes in the brain over the course of a season and even a single game. The researchers needed to determine if the concussion caused saliva changes above and beyond the repetitive impacts. Concussions were diagnosed in 106 players in the study, while 50 players were assessed but determined not to have a concussion.
The saliva was examined for molecules called microRNAs. Previous research has suggested that different levels of certain microRNAs are expressed in individuals with a traumatic brain injury. In this study, the researchers found that a panel of 14 different microRNAs together distinguished athletes with a concussion from the non-concussed athletes with 96% accuracy at the post-game time point. Certain microRNAs continued to show differences at the 36-48 hours post-game time point. Others showed significant changes across time points, potentially giving information about the underlying physiological processes happening after a concussion.
What does it mean for current athletes?
While the potential for saliva biomarker tests to diagnose concussions is an exciting development, it will be a while before this technology is on the sidelines of every high school football game.
First, far more research is needed. The findings need to be replicated with more studies in male athletes. It also needs to be studied in different populations. For example, biological differences may make the biomarker profiles different between male and female athletes. The normal processes occurring in the developing brain of children and adolescent athletes may also affect the way the microRNAs are expressed post-concussion. Some of this research is already underway.
Another issue lies with where and how the tests are conducted. While the saliva sample can be easily acquired on the sideline, the test can only be run in a lab setting at this time. The test could still be useful for diagnosing concussions in athletes, but it wouldn’t help with in-game return to play decisions. There is a critical need for objective sideline tests, as those who continue to play after a concussion are at a greater risk of prolonged recovery, over five days longer on average, than those who leave the game immediately after the concussion. It would also be financially and logistically challenging for high schools, middle schools, or youth athletic associations to purchase laboratory equipment for testing or store samples and transport them to a lab within a reasonable amount of time for testing. Although future technological advances will likely overcome this barrier, the current need for laboratory testing is a significant limitation for the practical utility of these tests.
Future studies will also need to examine the changes in microRNA over time. Changes were observed in the microRNA profile between the three time points. Some of the microRNA biomarkers may recover to baseline levels quickly, while others may linger. This has two important implications. First, the test may not be as accurate, or effective at all, if the evaluation is conducted several hours or days after the concussion occurred. Second, it isn’t clear yet whether or not these biomarkers will be helpful for tracking recovery from a concussion. Return to play decisions in the concussion recovery process still depend largely on athlete report of symptoms, and some athletes may say they are symptom-free when they are not so they can get back to play sooner. It’s possible that certain microRNAs or combinations of them may also be biomarkers of recovery, but more research is needed to make that determination.
What could this mean for the future of concussions in sports?
Although saliva microRNA tests aren’t ready for widespread commercial use yet, it seems likely that these tests will become a critical part of concussion diagnoses in the future. A handheld device that could quickly and accurately test the saliva on the sidelines would give clinicians an objective way to diagnose a concussion and remove athletes from play even when they deny their symptoms.
Concussion education and behavioral interventions will still remain a critical part of diagnosing concussions. Some athletes show obvious, noticeable signs of a concussion, but that isn’t always the case. The saliva test won’t be helpful to diagnose a concussion in an athlete who isn’t evaluated because they never report their symptoms.
It is also important to note that no single test is perfect. Even with a 96% accuracy rate, four out of every 100 concussions would be missed. Just like with computerized neuropsychological testing, like ImPACT, no single method should be used alone to diagnose a concussion. The researchers who conducted this study were careful to point out that the use of these biomarkers and other components of the clinical exam are likely related to each other and intended to complement each other. However, one is not intended to replace the other. If a patient is displaying clear impairments or has symptoms suggestive of a concussion, even if the saliva biomarkers are normal, the athlete should be considered to have a concussion and removed from the game. When in doubt, sit them out.
This new research is likely an early step towards the future of diagnosing concussions with an objective, easy to obtain saliva test. It is a exciting step forward in concussion research. Yet, critical steps still need to be taken, including research in different populations and the development of a sideline tool to test the samples. Thus, headlines like “New Saliva Test Can Quickly Diagnose Concussions” are true, but somewhat misleading. While the test does seem to quickly and accurately diagnose a concussion and shows great promise for the future, it won’t be showing up in your athletic trainer’s kit on the sidelines any time soon.