S100B is a serum protein that is thought to aid in the functioning of neurons early in life, and it is present only in the brain. In studies over the past several years, the S100B protein has been found to be transiently increased in the bloodstream after mild TBI (Dash et al, 2010), suggesting that the blood-brain barrier can be compromised in traumatic brain injury, including concussion. It has been evaluated in six clinical trials with over 2000 participants and demonstrated 98% sensitivity in the diagnosis of mild TBI.
The blood-brain barrier (BBB) is a separation of circulating blood from cerebral spinal fluid in the central nervous system (CNS). It is semi-permeable, allowing some materials to cross, but preventing others from crossing. The blood-brain barrier protects the brain from many common bacterial infections, antibodies, poisons, and certain drugs.
When the S100B protein becomes present in the bloodstream, the body may react to it as a foreign invader and release auto-antibodies to attack it. The antibodies can then leak into the brain through the weakened blood-brain barrier where they are thought to attack brain tissue. In one recent study, four out of 27 football players who had pre- and in-season blood tests showed signs of an autoimmune response to elevated S100B levels.
In the future, testing for the presence of the S100B protein following suspected concussion may be one way to rapidly confirm the injury. In 2010, the U.S. Army announced that 34 patients had been accurately diagnosed with traumatic brain injury via a blood test for other proteins (SBDP145 and SBDP120) that seep through the blood-brain barrier after damage. The Army data focused on mild to severe injury, so ongoing S100B studies might help create blood testing technology to detect mild brain trauma quickly and perhaps for as little as $40. S100B blood tests are already used outside of sports, and as a standard procedure in a few emergency rooms in Germany for diagnosing brain trauma.