If in doubt, sit it out. That’s currently the best way to ensure that a concussion isn’t made worse by a second head impact. But it can be a tough call to make, particularly for a professional sportsperson whose career could hang on how quickly they get back on the field. What if there was a simple test using blood or saliva that could be given within a few minutes of a suspected concussion to provide a definitive, reliable answer as to whether a player was concussed or safe to rejoin a match? It could also be used regularly in the days and weeks after a concussion to determine exactly when the player had recovered enough to return to the sport.

A bedside – or in this case, field-side – test is a key area of concussion research. It has become particularly important in recent years with the growing understanding of the more serious long-term consequences of repeated concussions.

Developing such a test involves finding a suitable biomarker – something released into our body fluids in response to a head impact. The challenge is determining which specific biomarkers and their ‘amounts’ are unique to concussion.

Concussion testing: S-100B

It’s still early days, but there are already some promising candidate biomarkers that could form the basis of such a test. For example, there are already blood tests in use for TBI, such as the S-100B test. However, this looks for a marker of more serious brain injury, the kind that would need neurosurgery. On a sporting field, that sort of injury would be obvious enough that a blood test wouldn’t be needed.

A distinctive physiological feature of concussion is damage to axons – the main shafts of neurons – caused by the shear forces associated with a knock to the head or whiplash movement.

Concussion testing: Tau

Professor Henrik Zetterberg, a neurochemist from the University of Gothenburg in Sweden, has been looking at indicators of axon damage that might meet the criteria of a marker for more subtle brain damage. He says that, so far, research has singled out two key candidates. The first, the protein tau, is already making a name for itself as a biological villain of other conditions such as Alzheimer’s disease.

Research has shown that amateur boxers have higher levels of tau in the blood stream the week or so after a bout, even if they’re not knocked out. These levels then slowly return to normal around eight to 10 weeks after the impact, as long as the boxer doesn’t have any more head impacts during that time.

Similarly, a study by Zetterberg and his colleagues, conducted among Swedish ice-hockey players, showed that tau levels were elevated in the blood after a concussion when compared to measurements taken at the start of the hockey season. They also found the levels of the protein S-100B increased following a concussion, although not nearly as much as tau increased.

Research has also found a correlation between blood tau levels and the severity of a TBI, where levels were higher in patients with a poorer outcome following injury. These studies suggest the potential for tau to be used as a diagnostic indicator for concussion.

Concussion testing: Neurofilament light protein

Another promising biomarker candidate for concussion is neurofilament light protein. Like tau, this is also a marker of damage to axons. Levels seem to peak four to 10 days after the injury, but unlike tau, neurofilament light protein levels are raised in the cerebrospinal fluid. This liquid cushions the brain and spine, and samples can only be taken in a sterile hospital setting. The challenge now for researchers is to refine the tests for these biomarkers and use them in combination with imaging techniques in order to better diagnose concussion and assess when it is safe to return to play.

 

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Damage to the brain as a result of a head injury. A severed axon (above), shown in the centre of the illustration, prevents impulses travelling from one neuron to another. Blood vessels can also be torn during head injuries, and the resulting bleeding causes a compression of the axons with the risk of a coma.