Blood Tests to Determine Brain Injury Unlikely to Move Forward

A blood test to detect traumatic brain injury (TBI) may not be plausible because of brain damage, according to research published in the Journal of Neuroscience.

Researchers from the University of Rochester Medical Center (URMC) evaluated mice to understand how the brain deals with waste, or what is called a glymphatic system. In 2012, URMC research demonstrated that the brain has its own unique waste system which is made up of a type of plumbing network that can use the brain’s blood vessels to pump cerebral spinal fluid through the brain to flush out waste. The waste flows from the brain into the lymph nodes and then eventually heads toward the general blood circulation system. From there, it enters the liver and can exit the body.

In the instance of TBI, proteins can shake free from brain cells, which can create this waste. But the researchers determined that the waste can impact the ability to measure the levels of proteins after they have entered the blood stream. From this, physicians were hoping to be able to determine the existence and/ or severity of TBI.

The URMC team experimented on TBI mice and tested the animal’s blood for 3 specific proteins — called S100 beta, glial fibrillary acidic protein, and neuron specific enolase) – which are often considered blood biomarkers for TBI. Alterations, which may stem from TBI, can impair the brain’s ability to remove waste. Prior research has indicated TBI can interrupt the glymphatic system.

“These findings show that a blood-based biomarker for TBI is unlikely to be effective for routine clinical use,” said lead study author Maiken Nedergaard, MD, DMSc, in a press release. “Both the injury itself and the clinical approach to TBI can impair the ability of the brain to remove waste, resulting in variable and — for the purpose of detection and diagnosis – unreliable protein levels in the blood.”

Human TBI patients in hospitals are often subjected to doctors’ neurological evaluations, which the authors commented can interrupt their sleep. Some patients are introduced to sedatives post tests, which can alter the amounts of proteins found in the blood. This is especially important because the glymphatic system primarily functions while humans patients sleep, the authors said.

“This study shows that even small changes can modulate the brain's ability to clear waste,” said Benjamin Plog, an MD/ PhD student in Nedergaard’s lab and a co-author of the study. “Consequently, we need to recalibrate our efforts and begin to think about measuring brain damage in a manner that takes into account the level of impairment to the glymphatic system.”